1) Is it possible to create an edition of D&D that could largely satisfy 90% of the player base?
2) If it's not possible now, was it possible in 2007, before 4e was released?
3) If it's not possible (now or then), what should Wizards, or whoever owns the D&D IP in the future, do about it?
1. Hell yeah - to take one from Dungeoneer, listen nerds, don't be so pessimistic!

Now 90% is a bit high of a number, but if we replace it with "the larger portion of current D&D players" then yes, I think so. There is a small portion of grognards that are happily settled into the OSR ghetto and will likely never leave, but we're talking about less than 5% - probably much less. Negligible, at least in terms of the overall community. Anyways, everyone needs and eccentric old uncle
But to really bring the community back together would require a Herculean effort on WotC's part, including admitting their mistakes even to the point of saying "We stand by 4E as a superior game to 3.5, but we admit that we should have playtested it more, should have opened it up to the fan-base, and should have gone a bit further with Essentials and really improved on the game, and we also realize that we left some really essential things behind with 3.5 and other editions." Etc. A little pandering to the diehard core fan-base would be rather timely at this point.
2. First of all, it wasn't nearly as fractured in 2007, afair. Sure, there were tons of d20 stuff but it was all under the umbrella of 3.something. In some sense you could say it was more of a
differentiation, a healthy fracturing, whereas now we have an unhealthy fracturing - not just the relatively minor in-fighting and squabbling, but the weakening of the core product (4E) which de-stabilizes the entire montage of D&D variations.
3. For one they could hire me as a consultant

. But I
do think it is possible, just very, very difficult.
What
I would do would be to get to work on 5E, but cast a wide net through the D&D fan-base--with a focus on the diehard core, like the folks here at EN World--and find out what they (we) want. As some have said, the rules themselves are secondary to the feel. People want to feel like they are playing D&D,
their D&D. A suitably flexible rule system should be able to accommodate that
and be a template for other variations, even 21st century ones like tabletop World of Warcraft or however WotC thinks they might be able to appeal to the young 'uns.
Ithink that 4E is both a positive evolutionary development from 3.5was, overall, an improvement on 3.5, but also a less finished and more imperfect product. It was like taking a more delicious cookie out of the oven too soon - it was a better cookie but it wasn't done cooking yet. WotC needs to recognize this fact, even admit it publicly, and then take it a step forward. It is time to really start work on 5E and make it the Edition of the People.