Honestly? Not much, I think. At least nothing that would find widespread appeal. But I'm fine with that. I have more systems I want to run that I find much more palatable these days. I'm just not WotC's target audience (anymore)
For me to re-embrace official D&D, they'd have to "power down" the whole thing, remove the magic from most of the classes that have magical subclasses, remove feats for all but pure melee classes, and cut down on the number of weird races by at least half.
I know, I know, I'm old-fashioned, but I'm fully aware of that. I also don't like the current, almost Victorian aesthetic of the artwork.
Something like "Hyperborea" (formerly AS&SH) or "Castles & Crusades" is much more to my liking, but D&D going that route is highly unlikely. Thankfully, those games already exist, so no hard feelings.