I skimmed through the thread and didn't catch who said it, so sorry for not giving credit, but the most salient point I've seen so far in this thread was something to the effect of, "people love the game D&D. What they hate is the company selling it."
It's worth pointing out that most of us here on ENWorld - using FORUM software - so 20 years ago! - are "grognards" and have been playing the game for a long time... but every metric I've seen says 5E is the best-selling D&D edition ever, which means a lot of younger people have come into the hobby.
There is a lot of talk out there how "the core D&D audience is cis white dudes that are middle-aged or older" - in other words, people who overlap a lot with the ENWorld audience. Like any group, we kind of self-select hanging out (here on ENWorld) with like-minded people, so we tend to create an echo chamber and think D&D ought to cater to what we want.
That's a dangerous assumption. However, if you look around online at who has been responsible for bringing most of the new crowd into the hobby, at least from what I've seen (YMMV), it's a lot of... 40-something white dudes (usually named "Matt" - Mercer and Coleville, for example) posting stuff on social media that resonates with the younger gamers and draws them in.
So while the 40- to 60-something crowd may make up the majority of D&D players, I do think that by and large their enthusiasm has contributed to the influx of people into the hobby. And from what I have seen, the new, younger generation of gamers generally relies upon the experience - and, to be honest, money - of the old crowd to get them started (most new gamers might be able to afford their own dice, but a lot can't afford the core rulebooks, much less adventure modules, campaign settings, etc.). In addition, because the 40- to 60-year old crowd are your thought leaders, and they're the ones that homebrew and were affected by - and most vocal against the changes to - the OGL, you ignore them at your peril. Finally, you need them to guide new gamers in because, to be frank, I would argue that D&D rulebooks are less accessible than ever - in the interest of granting older gamers interesting choices, you overwhelm new gamers by the sheer number of pages they have to read (I compared in another thread reading the current PHB/DMG/MM at nearly 1,000 pages of dense text with reading the old Mentzger Basic Set at about 100 pages of much less dense text).
All of that was a long way of getting to, "while 40+ year olds may not constitute the majority of your players, they probably constitute the majority of your revenue stream right now" - they have the money to buy your books and the expertise to use them. In addition, they are the "gateway" to new revenue, so you have two big priorities when you start.
1. Keep the 40-60 year old crowd happy in the short term. This means releasing as much as you can under the OGL and opening up all of past settings not currently in active support for fan releases. You're not doing this because it's going to bring you a lot of short-term profit. You're doing this because NOT doing so will both drive away your biggest spenders and dry up your flow of new players.
2. The most important thing medium term is coming up with an introductory product with very low barriers to entry. And by "low barriers to entry" I mean "low price point" AND "low complexity of rules." This allows new players to find your game without being gatekept by your current "most important" group, and allows you to start a line you can design for without being totally to keeping your current customer base happy.
Unfortunately, to keep this product compatible with the "flagship" product you are producing for the 40-60 year olds, this probably looks like a very stripped-down, partial version of your rules. (Here I am looking at the Pathfinder Beginner Box as a great example - everything in the box is PF2E, but you only have 3 ancestry/race choices and 4 class choices instead of the 7 or 8 and dozen-plus in the PF2E core rulebook).
It could also look like a VTT/software product (I'm going to shorten to "VTT" here but I'm also considering a built-in electronic "bookshelf" as part of this product) where the most basic rules are free (or close to it) and where there is a micro-transaction cost to add each new race, class, etc. This is going to infuriate your 40-60 year old crowd, so you probably have to introduce this as "free basic rules" and instead of "microtransactions" at first (e.g., to add the "Barbarian" class), you introduce things in larger content bundles (e.g. $20 for the "martial expansion" that includes all barbarians, monks, rangers, paladins, etc.). Your basic rules need to be extremely simplified and probably include one or two "solo adventures" for players to learn the basic game mechanics with.
Having a VTT able to dynamically produce a bespoke "Players Handbook" that covers only the ancestry/class combination a player picked would be exceptional too - instead of having to consult the PHB and having to leaf past all of the content for ancestries/classes you aren't using, you can consult a "limited PHB" that's bespoke to the combination you're using (no cleric spell lists included if I'm playing a bard).
Your VTT also needs to be able to allow your friends to see (but not export) content you have purchased while you're playing at the table - so only one player needs to buy the "Barbarian" pack for everyone to understand what the Barbarian does... but if you and your Barbarian aren't at the table, and someone else wants to play a Barbarian, they're going to have to spring for the content pack. This is where the money comes into play (and where you have to be very careful with how this is presented so as to not upset your 40-60 year olds, and again, I would contend if you've made it clear the "Core Rules" are free and that you're only up-charging for "optional extras" you might actually be able to get some of them on-board... provided the extras are balanced with the rest of the system so it's not Pay-to-Win).
Once you have figured out your "core" rules, you need to have a schedule for releasing a steady stream of additional content on a yearly basis. We've seen this sort of thing with focused splatbooks over the years (starting in 2E mostly though 5E seems to have gotten away from focused splatbooks), and you might actually have two separate release tracks... one "core rules" track that releases "generic martial packs" or "generic arcane packs" and one "world-specific" track that releases content customized for specific campaign worlds (e.g., one "Wizards of Thay" for FR, one release for Dark Sun, one release for Ravenloft, etc). This probably also requires putting emphasis on developing and differentiating campaign worlds (I would say at least three, possibly more).
Once you have your software/VTT you can also use that to run your "adventurer's league" or what have you where DMs are allowed to sign up to run your AL adventures; perhaps you offer them "Adventure 1" for free, and if they run an arbitrary number of players through the adventure (let's say 8; i.e., run the adventure for a party of four players twice), they get free access to "Adventure 2" and so on. Adventures in this path might be released quarterly. Other adventures and setting-specific adventures might be released in other months and be available for a fee (or a subscription).
Again, the "free" path is your loss leader to try to hook players into trying additional stuff.
Having put this path into place, I need to concentrate on hiring the following (and there may be some bleed among roles, for example, a creative writer might have some ideas for mechanics, and a game mechanics designer might have some creative ideas for a setting, but if the creating setting writer has a mechanical idea, s/he should pass it off to the mechanics designers and work with them to ensure the mechanic is well designed while retaining the lore flavor rather than writing mechanics himself/herself):
1. Game designers capable of coming up with multiple permutations on the same basic mechanical ruleset (so they can release "expansions" on top of existing rules). I have a few names in mind, but I won't name them specifically here as that will cause this thread to devolve into the relative merits of various game designers. Assume I don't get your favorite, but I get a group that you feel is "competent" if not superstars at design.
2. A programming division capable of translating these rules into a VTT/software "bookshelf" experience that is intuitive. This is HARD (and might be why we've seen Microsoft folks brought into WotC leadership lately).
3. Several creative setting writers whose job is to come up with the fiction for various settings old and new. They will be responsible for setting lore.
4. A few continuity folks to ensure the setting writers produce material that is internally consistent. In a best case scenario, each continuity person is an expert on one setting (so they don't conflate them).
5. Adventure writers. This is a different skill than mechanics design or lore design. Their job is to take the mechanics from the game designers and the settings from the creative writers and synthesize the "crunch" from the first group with the "fluff" from the second group atop a solid adventure (kind of similar to level designers in video games).
6. A lead fantasy artist for each setting we decide to make so that each one has a visually distinctive style that AI art just can't give you (think DiTerlizzi's Planescape, Elmore's Dragonlance, Brom's Dark Sun, Reynold's Golarion, etc.).
7. I agree with the previous sentiment about reinstating Dragon and Dungeon Magazines, and those should probably be used as they used to be - unofficial recruiting tools for new talent to showcase their abilities before being hired on full time.
That's probably more than a 3-year plan, but I think it gives you an idea of the direction I'd go... and unfortunately, it does start pushing away from "physical books" and more to "mobile devices" but that's the way the new generation plays, and while I wish they'd cater to me and my old grognardness, even I use PDFs far more than physical books any more, and any realistic business plan for D&D is going to have to bend to that reality. That said, I would also create physical books and sell them at full MSRP (so as to not undercut physical bookstores) ... but any physical book ordered direct from me (or WotC or whatever) would always include a PDF with an electronic watermark (here I am not thinking of the way it is currently done with your order number or name printed on every page; instead you should have a way of sneaking an identifier into the file structure itself so that if the PDF gets leaked, you can identify the leaker). This way there is an incentive to buy physical books directly from me (the PDF/VTT version) but for the "Physical Book Only" crowd, your bookstore/FLGS of choice remains a viable option (and if they want to undercut me a bit on price for physical books, so be it, since I can add value in the PDF/VTT version they can't).
