I honestly don't think a new rules set is going to be what brings people back to D&D and WotC, and it certainly won't bring me back in. It will definitely help for WotC to put out a barebones game system that can accommodate the vast array of material already out there, but primarily they need to be looking at ways to bring the gamers back into the fold.
So, what will?
There needs to be a new renaissance of sorts that brings all these amazing products coming out under one roof.
I'll re-post something I put up on Google+.
WotC needs to harness the exact power that's killing them: individual creativity.
D&D has always been about that, with homebrew worlds, campaigns, adventures, monsters, etc. It's just, people didn't really have a way to publish to the masses.
With the OGL and so many different creations out there that take advantage of it and the ease of internet publishing, now WotC isn't just competing with Paizo or whatever, but all of the amazing creative minds out there. Just take a look at all of the amazing, talented work coming out right now. Why would I buy the next generic WotC adventure when I can buy Hammers of the Gods?
So, what can WotC do? They can "publish" it all.
Create D&D Next as a hub for all that content. Create a barebones, lean and clean system that can be hacked to pieces and then provide a sort of "App Store" for D&D Mods / Hacks / Adventures / Settings / etc. And, use an App Store-like system for ratings, reviews, featured content, etc.
There are some hurdles of course. They'll need guidelines on PDF design and logos and all that. But, people were fine using the OGL - why not this system? And, instead of leaving the OGL out there for someone to make money off of the game without WotC getting a cut, WotC can actually profit by taking a small fee for each transaction in exchange for the server space and distribution (like Apple does with the app store).
People are creating it anyways, so why not give them the tools to get it to the largest audience? Imagine if the next Into the Odd or Tales of the Grotesque and Dungeonesque or Lamentations of the Flame Princess or Adventurer Conqueror King were simply modules for D&D Next? Now, those creators might not actually go that route, but there are certainly people out there that might take advantage.
In truth, right now there are so many different variations of the game that making yet another variation with dozens of splatbook modules just isn't going to cut it. People are going to other sources for their D&D stuff.
So, what will bring me onboard with D&D Next?
It won't be whether D&D Next has healing surges or not... Or, Vancian casting... Or, whatever.
What will likely bring me into the fold is if WotC created an umbrella of inclusion for all types of gameplay and ideas and settings and modules and rules variations that is easily accessible by everyone and allows people to get their ideas out there. That won't be through rules, it'll be through something bigger than that.
There should be no D&D "Insider", because every single D&D player of one sort or another, from OD&Ders to 4Eers should be included and allowed to share ideas and concepts. Then, let each DM or player pick and choose what they like for their various styles. But, there's a central nexus where we all meet and exchange these ideas.
And, that's the future of D&D to me.