I for one hated the idea of 3rd edition. I spent way too much on my second edition addiction, but once I got the 3rd edition PHB for my birthday I couldn't look back. One major difference between the 2ed to 3ed transition and any future version transitions is the OGL, it's another thing for WOTC to consider.
Will they update it too, or leave it, how much resistance will come from 3rd party publishers about a completely new edition, just look at that new 3.0/3.5 dual compatibility logo for proof of resistance to the 3.5 change, and its not even really a change. If WOTC does go 4th edition, could 3rd parties continue to print 3.5 if the SRD was changed, I'm not a lawyer but I think they could. So even if WOTC does go 4th edition there is no guarantee that 3rd party publishers will go to 4th edition. WOTC could kill themselves with a new edition if the 3rd party publishers didn't go for it, and continued to publish 3.5, which given its publisher and community support, could continue and provide competition for 4th edition, WOTC would be competing with itself in a sense. So from a business perspective I think its risky for them to try, because the OGL added a whole bunch more variables to the new version debate.
I'm all for these backwards compatible revisions, I think the 3.5 idea is great, make a great system even better. If 4th edition was something similar, backwards compatible and just another refinement, or it was 3.75 or whatever, then I might be for it, but a whole new version, I can't see it happening for a long time, maybe even beyond the life of WOTC. Maybe it's just wishful thinking, since I don't want to make my 3rd edition collection as "useful" as my 2ed edition stuff is today, but I really don't see it happening soon.