It could cease to exist.
Seriously.
It's not to everyone's taste, but 4e is far and away the best at what it does, and is actually a unique entry into the market. Let 4e "be D&D" for a decade. Reprint old systems occasionally, maybe, but the community doesn't really need 5e. I've seen NOTHING from the 5e playtest that made me want to use it over anything else I have on my shelf RIGHT NOW.
If I want fast, easy-to-play rules that don't totally sacrifice tactics? Savage Worlds nails it. If I want "classic" D&D? I've got hundreds of megabytes of OSR retroclones on PDF, print-on-demand, and my Rules Cyclopedia. If I want a more modern take on "classic" D&D, I've got Pathfinder (with excellent GM material from Paizo) and Fantasy Craft (which frankly blows every other d20 system out of the water). If I want "gritty" fantasy, I've got Runequest / Legend.
But if 5e is going to have ANY chance of winning me over, it needs to be FAR AND AWAY the most deeply supported version of D&D EVER. It needs to be OGL. It needs to allow third-party publishers to create supplements, modules, and settings. It needs if not innovative at least COMPETENT digital support. It needs to be available on PDF so I can use it with my Android tablet. There needs to be so much cool stuff available for it that I can't HELP but want to buy it. Every time I walk into my FLGS, if I'm not tempted to walk out with $100+ of D&D Next stuff, then it's a failure in my book. I've probably spent $700-800 on RPG stuff the last 24 months. Other than a $20 set of dungeon tiles, not a cent of that has been on WotC stuff.
I forget who said it in another thread, but it's absolutely the truth--I don't need D&D Next, but it definitely needs me.
In order to win me over, 5e needs to be significantly better at providing me with a D&D experience than my current edition of choice (3e). As for what that actually means, it is both ill-defined and necessarily subjective - I'll know it when I see it.
In particular, I'm not particularly interested in 'modularity'. If I have to make significant changes from the Core, whether these are house rules or are the "official house rules" that modules represent, the game will quickly reach a point where it's just not worth my effort. I know that's a very demanding requirement, but there it is: the Core needs to nearly match my requirements in order to win me over.
I realize this makes me part of a very, very, (very) small minority in this part of the realm. Most people will want to be able to just open a book, grab the stats for a zombie, and go with it...and they will want it to be the same zombie stats that their friend used in his game last weekend.
And I also realize that my idea will not work at all from a sales point of view; Hasbro wants (needs?) to sell textbook after textbook full of monsters, races, classes, and everything else. It is not in their best interest to give us the tools we need to build for ourselves the things they hope to later sell us.
Miniatures. Painted. With stat cards. And the foes should be ready to run from that card.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.