I think we’ll see 5th edition D&D; in 2013, or 2012 if sales decline faster than expected. 5th edition will be the next iteration of 4th edition, as tightly related to it as 3.5 was to 3.0. This new edition will have no OGL or GSL.
When 6th edition rolls around (in, I dunno, 2016 or 2017), it will abandon the 4E structure entirely and go back to something closer to 1E. This will be accompanied by a huge nostalgia-based marketing campaign. Vancian magic, a PC assassin class, and half-orcs and gnomes as core races will return with great fanfare. The marketing message won’t bag on the 4E/5E era specifically, but will use the phrase “returning D&D; to its roots” so often that fans of the then current game will feel alienated. To further reinforce the message, there will be rewrites of classic modules like the GDQ series, Dragon Magazine will be relaunched in print form, and Skip Williams will return to write Sage Advice.
What happens after that? Answer hazy, try again later.