One reason the 4e / 3e split was so divisive, I think, is because when the 4e fans threw up their hands in joy and said, "FINALLY!!! CLASS BALANCE!!", all of us 3e fans went "Huh? Really? THIS is the game you wished you'd been playing for the past 25 years? Hmm. Didn't see that one coming." The concept that entire groups of players would so wholeheartedly embrace 4e's conventions seemed almost foreign to the 3.x-ers.....and the 4e-ers couldn't for the life of them figure out why the 3.x-ers couldn't see that the mechanical improvements were producing a "superior" style of game.
I don't disagree.
The problem with 4e is the limited play style, the limited range of campaigns and story emulation. If you want to play a heroic fantasy game with high magic and dungeons, then 4e is a really, really good choice. The problem is that isn't not the best game for everyone. And because it wasn't the best choice, people dismissed everything related to 4e. Suddenly good ideas such as class balance and choices in combat and the like became the purview of the enemy.
It's human nature to oppose the road not taken. If you can buy a PS3 or Xbox but not both, so you justify your choice by continually deriding the other, finding reasons to hate.
It's also very North American. The US is a culture of extremes, driving people to binary options: yes or no, left or right, red or blue, republican or democrat, north or south, right or wrong, with us or against us, star trek or star wars, TOS or TNG, apple or PC, Ford or Chevy, etc.
And, of course, 3e or 4e.
When, really, like any game system, you can play both when it suits you. If I ever run a game set in
Dark Sun I'll probably use 4e because the two work so well together. But
Ravenloft is a terrible fit and you might be better off with 3e. And
Dragonlance is built on the conventions of 1e and the original adventures play best with that rule set.
As you mention, the problem is luring people back to a generic rule set from games that cater to them. 4e players are the worst in this respect. They had THE game built for them, it fit them so well, and there was so much crunch for them. Contet was being produced on a daily basis at one point.
Now they don't want to share. Look at all the threads rejecting even the slightest hint of older editions. Look at the reaction to Essentials that was still very, very 4e but had a dash of older edition design for flavour.
Both sides will need to compromise for the base game, there needs to be a give and take.
I don't see Next doing well. I foresee D&D Last. Not because the game won't be good, but because people are selfish and cannot share, because four years of favoring one play style spoiled an audience and they won't let go.