I'd start with a much smaller set of core rules, presented as a boxed set of six or so booklets: core rules, classes, equipment, grimoire, DM's guide, and Monsters.
But for an awful lot of it, software is a likely way to do - again, ideally in a form that some/all of it can be downloaded for offline use.
But that's all just me thinking out loud - I haven't thought anything through in detail, I'm sure it's full of holes, and it would probably suck anyway.
So like how D&D originally came.
I was actually recently thinking about trying to put together my homebrew campaign into a "Source Book" and I had the idea of instead making it a collection of booklets. Things I could print out and staple like a Zine. Instead of one big book, break everything up into it's own booklet. The starting village gets it's own book, including a map, NPCs, and maybe a basic quest or two.
Then the High Level Wizard NPC who is a patron of the party gets his own book. It goes over him, his tower, his personal introductory quest..
Any major faction gets their own booklet. Each core quest gets it's own book, etc.
I thought this would be really neat just to see all bundled together as a box set. Then when you're running it at the table, you only need the relevant booklet or two. While it seems novel it also feels tedious. Having to reference other books. Sure Guard Captain Oren is described in the Quest Book where he's relevant, but maybe I want to give him a retinue of 6-8 guards to accompany him. Now I need to go find the RorSkellian Military Faction booklet.
I don't know. I think it'll be a fun project to do for myself, but I'm not sure it would be a great idea for a product.
I could see a big benefit to doing the core books like this though. One player is rolling up a new character so they have the classes booklet, someone else is shopping so they have the equipment one, a third player is picking out their spells to prepare so they have the spell booklet.
Plus it's so easily expandable. They could put out new class booklets, new monster booklets. A big monster compendium where they are broken down into either challenge rating or perhaps setting/environment?
And Digital is great for RPG material. I love being able to clip up my monster book and save just the pieces I need for my notes, and to reference at the table. but I still like to sit down with my physical book and read it for ideas. I also think the market is held up largely by RPG collectors. I think a lot of us buy a lot of books we never actually use, but we like having them to skim through to mine for ideas or to dream about actually playing.