Osgood
Hero
I think there are plenty of good ideas in here so far, and honestly, I wouldn't complain about any of them. But I think a lot of this discussion is backward-looking, which we've already seen plenty of over the past 10 years (with at best, mixed success--Eberron was well done, Spelljammer not so much). I think this role is going to be focused on new worlds, and I'm all for that. The trick is to not fall into the trap of 90s era TSR and splinter the audience, where each setting only captures a small part of the fanbase.
So, to answer the original question, I think I would try to think outside the box and try a different approach. Come up with some new settings, but rather than produce a big Campaign Setting Book, I might make a book that focuses on a theme, style or environment rather than a full setting--could be an environment like desert or swamp, could be thematic like unexplored frontier, fallen kingdom, or oppressed dark land. In that book present five very fleshed out mini-setting--a kingdom or territory--maybe two from older settings, the rest brand new. Then include new monsters, and a few adventures that can be inserted into any of mini-settings.
Over the course of a few books, these worlds come into more detail (and over time they figure out which one are most popular). But if a DM isn't interested in the entre world, they can just drop the individual elements into their home brew world.
So, to answer the original question, I think I would try to think outside the box and try a different approach. Come up with some new settings, but rather than produce a big Campaign Setting Book, I might make a book that focuses on a theme, style or environment rather than a full setting--could be an environment like desert or swamp, could be thematic like unexplored frontier, fallen kingdom, or oppressed dark land. In that book present five very fleshed out mini-setting--a kingdom or territory--maybe two from older settings, the rest brand new. Then include new monsters, and a few adventures that can be inserted into any of mini-settings.
Over the course of a few books, these worlds come into more detail (and over time they figure out which one are most popular). But if a DM isn't interested in the entre world, they can just drop the individual elements into their home brew world.