The contracts they had for the artwork, excepting as PDFs or straight up reprints in their original form, might prohibit selling collections and revised versions of older material. Once they get into needing some, most, or all new artwork, it becomes less attractive for them to revisit the older material in a new form.
Yikes, no thanks. Reboots and remakes are bad enough in Hollywood.
New stuff, please, not the same 80s stuff over and over again. New settings! I would love new settings!
OK, I get that you want to focus on the D&D franchise as a whole and story first and foremost. I get that if we ever see splats or campaign settings, that they'll be rare. I'm OK with that. I also get that you want your stories to be big, and that for financial reasons the 200+ page hardcovers work better than 32-page modules. OK, fine. But there's still a massive gap in the D&D line that I'm worried you won't fill, which is one-shot, shorter adventures - building blocks for larger campaigns, but not campaigns in and of themselves.
I have one possible solution for you. Leaving aside an OGL, here is the idea. How about produce a series of hardcovers - maybe one per year - that compile, adapt, and update the classic adventures of past editions. I'm not talking about re-writes or re-visionings like the 4E Giants book or Tomb of Horrors. I'm talking about taking the exact same adventures, re-formatting to modern standards, and converting to 5E - and then compiling them in a series of annual hardcovers. Now honestly, I'd just as much--even more--like to see new stories. But you already have a wealth of excellent adventures that could use a paint job and be presented to a new generation.
Each hardcover would have 6-8 modules, or around 200-300 pages (maybe more, but let's not be greedy). There are any number of possible themes, but the idea is that every year you'd produce a nice book that included many adventures. You could also provide guidelines on how to play them as part of a larger campaign. Some of the work is already done for you in that the adventures are already written. It would still require a lot of work, but not as much as just creating new content. A mix of old and new art would be nice.
Some possible books:
Basic D&D Classics - Keep on the Borderlands, Castle Amber, Lost City, etc
Dangerous Dungeons - Tomb of Horrors, Tamoachan, White Plume Mountain, Tsojcanth, etc
Giants and Drow - the famous Giants-Descent-Drow-Demonwebs sequence
Etc.
Now ideally we'd still see new stories, but this idea just seems like it would work on many levels, would appeal to old and new fans alike.
Make it so, Mearls.
Doesn't D&D suffer from too many settings? How does a new setting that has no discernable IP attached to it help Hasbro at all?
Jurassic Park just pulled in $200+ US domestic in a weekend. People love old stuff. People want old stuff. People pay lots of money for old stuff.
The contracts they had for the artwork, excepting as PDFs or straight up reprints in their original form, might prohibit selling collections and revised versions of older material.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.