5th edition:
Mages are as awesome and versatile as they were in 3rd edition, yet still balanced with everyone else and every other class is still fun to play. The ultimate balance is reached and everyone who loved 3rd for 3rd and 4th for 4th unites in the great gamer revolution.
Ahh...the Holy Grail of fantasy game design (or at least D&D): how to make mages awesome
and balanced. Actually, this is inspiring me to start a post on it...
My predictions...
5E will happen sometime between 2013 and 2015. It will be a genuine new edition, requiring people to buy all-new books, but it will not be a revision on the scale of 3E --> 4E, or even 2E --> 3E. It will be more along the lines of 1E --> 2E.
4E represented a gigantic experiment. There were a whole lot of new concepts introduced and the entire system was rebuilt from the ground up. Some of those new concepts worked well as designed, others didn't work so well but were fixable, and others more or less bombed. Essentials is an effort to fix what can be fixed within the system as is. 5E will address the rest.
Technology-wise, I think much will depend on how Cryptic's new Neverwinter Nights game turns out. I have a suspicion that WotC regards NWN as a replacement for the Virtual Tabletop we heard so much about a couple years ago. At this point, it's pretty clear that Gleemax* and the VTT have been written off as total failures; but if Cryptic makes a go of NWN, WotC will make a deal with them to build a replacement based on the NWN engine.
[SIZE=-2]*It still boggles my mind that somebody thought "Gleemax" was a good name.[/SIZE]
Good predictions, although I wonder about 2013--that would seem too soon, especially with Essentials coming out.
I wouldn't be surprised to see WotC find a smoother way to transition from one edition to another. As some have mentioned--including myself--the times of edition cycles may be at an end; Essentials may be the harbinger of "jumping off the wheel" and taking a different, more open-ended and gradual approach. This doesn't mean there won't be a 5E, but that by the time we get there it will be
relatively painless (and thus less controversial) because a bunch of incremental changes (through errata, D&D Insider, etc) will have gradually changed the game. "5E" may simply be a new round of revisions and formatting--the next version of the core books, with new covers, formatting, art, but still 4E compatible, or at least Essentials-compatible.
So if I were WotC I would try to find a way to make buying new rounds of books appealing without the resulting fallout. One way to do this is what they seem to be doing: rather than only making signficant rules changes with a new edition, integrate change as a regular and expected aspect of the game. D&D Insider makes this possible. A new "edition" of the core books is less like a total re-booting of the game and more like a "state of the nation" (or game) printing. It is a representation, in other words, of where the open-ended and ever-changing game is at a certain time.
To put it another way, I imagine that in the past WotC has compiled a list of changes they would like to make for the next edition of D&D. Rather than saving them up for that next edition, those changes can be (and are being) implemented more frequently,
within the current edition. So when "5E" comes out it is more of a marker for "the changes thus far" and thus more contiguous with all that came before.
If what I'm saying is true then we could see that sooner than later, maybe corresponding to your dates.