I love the old stuff that came out when I was getting started as a kid, but I think going backwards to resurrect Greyhawk, Dark Sun, Dragonlance, etc. is a distraction. So to settle the issue, I would announce free 100 page PDF settings overviews / recaps with conversion guides to go with all the PDFs of old adventures on DMs Guild. All the old settings are available to use on DMs Guild so the community can release new content. The Adept program is expanded to included some leadership for each of these old settings so that a community can form around them to promote the best stuff on DMs Guild. I make a clear announcement that there are no plans to release any official content for old settings in the future. Rip that bandaid off and move on.
Now on to new things…
I'd announce a new contest, but with a twist on what happened with Eberron. Instead of a full setting, submit a party with your best, most interesting, engaging and entertaining 5 characters of brand new 0th/1st level adventurers maybe with a brand-new class/sub-class to introduce some new mechanics at the same time. Backstories, personality, etc. Huge blown out contest with celebrity judges to pick the best ensemble. Winner gets a check, a contract to consult with the WoTC team for a year, and signs over all the rights. Not a story, just story hooks. No full-blown setting, just a starting location with one big hook that points towards where the party, and the world, is headed.
The in-house team goes to work on building a setting/world starting from this initial location, and a new story around the big hook. There is a slow reveal over a couple years that engages the community through new books, adventures, and con events. The setting becomes the foundation for movies.
This is also the moment to finally break away from racial mechanics entirely and let culture just be part of the story. Mechanics can come from individual choices about background and training.