I'm wondering how much this will be possible. To really make that happen would require an exceptional core game. It will be interesting to see what comes out though. I'm all for a more united community.
It is certainly tricky, but that's why game designers get paid the big bucks!
But seriously, there is no way that they're going to please everyone, but I think they can go a long way towards offering the "feel" of older edition play except to those that are super-attached to specific rules, who will always miss the forest for the trees and get hung up on the letter of the law rather than the spirit.
For instance, there is really no way to please those for whom the "Old School feel" is contingent on making a save vs. Polymorph and Petrification and an attack vs. Fortitude is a sin against Gygax. It is very unlikely that we're going back to that sort of hodge-podge rules system, just as it is very unlikely that eight-track players or rotary phones will make a comeback.
But it may be that there are more ways to get to Rome than the previously trodden path; that is, the "Old School feel" may be possible through other means including a stream-lined modular rules system that facilitates the type of game experience that was the hallmark of pre-WotC D&D.
I would suggest that the rules don't limit or force a specific type of game experience, but they do encourage (or discourage) a certain kind of experience. The main issue that many had (and have) with 4E is that for various reasons it was more difficult to create the type of experience that long-time D&D players associate with D&D.
The key then, in my view, is to create a 5E that doesn't focus on the past in any form--whether we're talking about OD&D, AD&D, BECMI or even 4E--but forms a strong basis for as wide a variety of D&D experiences as possible, while remaining connected to the overall legacy of the game. So if I were designing 5E I would make sure that, in the context of this discussion, all of the following were true:
*It is possible to play an "Old School-esque" game.
*It is possible to play a 3.5esque game.
*It is possible to play a 4Esque game.
*It brings something uniquely its own ("5Esque") to the table.
The key being that "esque" is less a function of the actual rules than it is what the rules are capable of facilitating. It is a subtle, but crucial, difference.