Count me among the folks that says 2-3 years, maybe an announcement at GenCon 2012 with a release in 2013, or maybe a year later. But I see 5E coming out in 2013 at the earliest - that's five years and doesn't sound quite as sheepish as four.
Lots of interesting thoughts in this thread. I do think that 5E will better integrate technology, but I don't think that paper books will be POD only. Maybe 6E or 7E, but by then there will be POD kiosks all over the place, maybe in some homes.
4E was a success in that it sold some books for WotC, but it was not a success in that it fractured the fan-base like no other edition before and probably was not as big a success as WotC had hoped, especially with the rise of Pathfinder. WotC hoped that 4E would come out and build up steam, but instead it peaked early on and then dropped, with a slight bump up with Essentials. We'll see if that holds or not.
Of concern, or at least interest, is the undeniable fact of the ever-changing 2011 4E lineup. It may be nothing, or it may be that WotC is in a state moderate crisis and trying to figure out what to do next. I wouldn't even be surprised if we get a year or two of minimalist publications while they develop 5E, in the meantime focusing on DDI and non-TTRPG D&D products like the boardgames and a MMORG.
But there will be a 5E, although it may be more akin to Essentials Revised, or E2. And 5E will be a golden opportunity to re-unite the fan-base. How? There are many ways, but I think one would be to re-integrate some of the things that have been lost - the emphasis on free-form gaming, taking away the (near) necessity of using miniatures, shortening combat, bringing the magic back to magical items, taking Essentials another step and further diversifying classes, and--for the love of every deity in any splat book every printed (regardless of edition)--making the game modular so that folks can play different versions of the same game/edition and still be "official." In other words, a Basic/Advanced format.
One thing that crossed my mind is maybe the Neverwinter Campaign Guide is going to be a transition product, a "Classic Realms" book that both pushes the Realms back pre-apocalypse, and segways the game into the next edition, sort of like the old Greyhawk Adventures did with 1E to 2E (Didn't it say that it was compatible with both on the cover?).
I also wouldn't be surprised if we see a 4E Revised before 5E. In other words, errata-ed, re-formatted, and revised versions of the core three, fully compatible with Essentials. Maybe that's why Sword & Spell is on hold.
In the end, WTFKs?