If I were to play at amateur brand analyst for a sec...
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What we have here is a problem of tribalism. Arbitrary lines have been drawn in the sand and people put themselves into mutually exclusive camps based on their "tribe." This is part of what creates the animosity. The Hatfields and the McCoys eventually just feuded because they'd been feuding -- it's a self-perpetuating process.
Tribes form out of a need for self-protection, when they feel threatened (accurate or not) from an outside force. Both sides of the edition divide feel threatened by each other, and so if they allow any leeway toward the other side, suddenly, their side "loses." "5e can't have ADEU, then I lose!" / "5e can't have Vancian magic, then I lose!"
So you then need to ask: how do we overcome tribalism? How do we overcome this fear of losing?
My first response is to take the issue off the table entirely by making sure that if someone wants a game that is exactly like 4e, then they can pay WotC to give them 4e rules.
The idea of selling PDFs from earlier editions is good. They should include 4e stuff in this, too. This shows that WotC is not interested in excluding anybody from the game. Re-publishing the 1e and 3e books is a good step toward this. I'd even advocate for them to license everything pre-5e as OGL, and, if they're already setting up a market to sell PDFs, why not make it a market that folks can self-publish on? Make your creation, make your label, slap it up into WotC's version of the "Apple Store," and sell it. WotC gets a cut of sales. You don't have to sell your 1e adventure on the WotC store, but if you do, your audience will be potentially huge.
You could even sell subscription models: pay WotC $20/month and you'll have access to the database of every official D&D book ever published. Maybe some online tools, too. You can download individual books for maybe $30 a pop or so instead, if you want to do that. Yeah, it's a bit of an over-charge, but that's why you have the subscription model, too: want to own, it'll be pricey, want to rent, it'll be cheap.
This isn't about 5e per se. This is about setting the stage for 5e by taking all the extremists off the table and giving them what they want: their own game, with new content for it, sold to them. Or just a collection. This removes the need for tribalism by essentially creating abundant resources. No longer do you need to worry about "losing" your favorite edition, now you always have it, and if you want new content for it...write it! Sell it! If it sells to the four people at your table, AWESOME!
It requires some infrastructure, but honestly a lot of the moving parts are already there. It benefits massively by making the resource of "rules for your preferred game" abundant. You don't have to take away from an ADEU controller fan to get your Vancian wizard, and you don't have to take away from a Vancian fan to get your ADEU controller. You both can have the game content you want.
When people say, "5e can do whatever it wants, I have enough 2e material from the WotC PDF store to last me forever," that's a good thing. That's one battle you don't have to fight. You don't HAVE to get the 2e diehard on board. If all they ever want is 2e, and you can set up a system that can profit from that (OGL it, sell PDFs for it, call it awesome), you don't care if they hate that 5e doesn't have THAC0.
5e can then be free to be the Edition To Rule Them All by being modular, and being forward-looking. It could be seen as The Final Edition, something designed to be modular because it is designed to be evergreen, changing, and self-contradictory. And when people get a little bored of their One True Way, or a little curious about this "advantage" mechanic, maybe they'll check it out.
In the matter of healing the edition rift, a new edition shouldn't be one of the first things you try. It should be one of the last things you try. One doesn't go climbing a mountain with two broken hands -- each hand will work against the other. Heal the hands, at least mostly, and then try the climb -- it'll probably go better.
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I don't know how much of that is viable, but I DO know that the need for each "tribe" to define 5e as "theirs" would be a lot less potent if they already had something they could call "theirs" that had some continual support. A compendium, A PDF marketplace, and an OGL D&D would address those concerns quite nicely. The reason the fight is so tumultuous is because people are SCARED, and with reason. WotC has had a better record of saying "tough noogies" to people who didn't like their direction than they have had of saying "Okay. Lets help you do it your way." The only way they're going to be able to actively support every edition is if they let other people do it instead, and just serve as a middle-man, and that's the only way they'll get Edition Warriors to leave 5e alone.
