I believe we are moving steadily in that direction, and I think it's a natural progression of WOTC's original development plan for 3E.
It was my understanding, based on comments made by Monte Cook and others, that the original plan with the release of 3E was to wait five years, release v3.5, then wait five years and release 4E. Even though v3.5 got moved up two years to 2003, the five year plan for v3.5 to 4E is still probably viable. That plan laid out books and developmental directions for covering the range of v3.5 products before 4E would be released. Even if WOTC got creative and added to the scheme, I still think we're in the latter half of that plan.
Now, WOTC won't do anything regarding 4E without making an announcement about it first, in order to build anticipation and win over buyers. The strategy I've always heard bandied about was a year's warning. I imagine that we'll hear something about 4E by Gen Con Indy 2008, if not sooner, with a release approximately 6-12 months after the announcement (and probably closer to 12 months).
If not, then I can see something akin to 2nd Edition's Player's Option rules set, a last ditch v3.75 effort released under some other label. It very well could be a D&D Saga Edition, if the Star Wars product is well received. If that happens, I think we'll have about 2-3 years after that before we see 4E on the horizon.
The rules are quite bloated and getting moreso all the time, with each new splatbook. It's only a matter of time before we see the next Player's Option/v3.75/D&D Saga Edition/4E version revealed at some big gaming convention.
At least, that's my opinion, based on the rules bloat I've noticed.
Of course, I've been totally wrong about things before, and it wouldn't hurt my feelings to be wrong about this, too.
With Regards,
Flynn