A few notes -
1st - The notion that D&D must change beyond any need to fix what does not work or works suboptimally because only then can D&D hope to bring in the number of new gamers that can keep the game and the hobby alive is unsupported.
3.0 and 3.5 have not proven so awful or damaged or broken that they are imperiling either D&D or the hobby. There is zero evidence to see a need to radially move away from 3.0 and 3.5 from this gross standpoint.
4.0 has not been widely playtested and vetted as 3.0 was and any market research that might suggest that new gamers will be attracted by 4e's changes is so under the radar that there is little to nothing to empirically suggest it exists. Rather, it seems 4e is Wotc's "hunch" about what gamers will like, old or new. Wotc's hunch is no better than anyone elses hunch who spends an equal amount of time considering the hobby.
2nd - As someone upthread noted, a 3.75 edition could well serve, as well or better than 4e as it is currently understood.
A 3.75 edition could better preserve the existing fanbase by maintaining greater continuity with prior editions while implementing change thought to bring in new fans. As it is, 4e is divisive, and if Wotc goes not get 3rd party publishers what they need when they need it, these divisions may yet grow wider.
A 3.75 edition need not be akin to the tweaking that was the 3.5 edition. It could well be sufficiently distinct to merit a 4.0 designation. Herein it is well to look at other games that go through edition changes with relatively minor changes but which are still judged to be sufficient for new editions by both company and fans. GURPS and CoC jump to mind as implementaing change but maintaining continuity sufficient not to divide the fanbase the way 4e is dividing D&D fans.
3rd - There is every reason to question matters now. Wait while saying nothing and 4e is a fait accompli. It is speak now or you're stuck with a 4e to which you gave up any chance to meaningfully comment.
4th - The whole notion that there is a HUGE audience for paper and pencil RPGs lurking in the mainstream, greater that that which now exists or which existed at 3.0's launch, is unproven at best and more like unto wishful thinking. Paper and pencil RPGs are destined to become model railroading, or board wargaming - once more popular but now popular at a much reduced level. Merely looking at the progress of electronic gaming more than strongly suggests that the pendulum has already swung well away from paper and pencil RPGs and its not going to be swinging back.
That 4e is intended to capture this invisible horde of converts to paper and pencil RPGs is laughable on it face. It is even more laughable that Wotc has what it takes to reach this market. What? They woke up in 2005 and suddenly realized this audience existed and that they could reach it? Hardly. If the audience existed, some evidence of it would have existed heretofore. Right now, that audience is akin to Big Foot sightings. And Wotc (and as successor in interest to TSR, to say nothing of continuing employees) has a track record of lauching RPG after RPG that folds. They wouldn't know mass market appeal if it came up and bit tthem to judge by their RPG track record. NOW, they suddenly have the Holy Grail of RPG design in 4e that will bring in the HUGE new audience and "save" the hobby? Look! Its Big Foot!
The fact is paper and pencil RPGs are past saving, in the sense of wide popularity, even to the level of the mid-1980's. Paper and pencil RPGs core audience is greying and nothing is going to reverse that as younger, potential players have far too many other options that offer as much or more attractions (note I did not say equivalent, as the P&P RPG experience has it unique characteristics).
Wotc should be aiming 4e at the 3X audience because that is nearly the limit of the audience for paper and pencil RPGs. Instead, 4e fixes what's not broken and is alienating/splitting the 3x fan base. This will only hasten paper and pencil RPGs inevitable decline.
If it ain't broke, Wotc should not be trying to fix it. Rather, they should fix only what _is_ broke with 4e. Sure, add some new stuff but not at the expense of so much of what's working just fine. Its not like there is a HUGE untapped audience who will be drawn to 4e. Its the 3X audience. Everything else is Big Foot.
In other words, 4e's audience is the audience for 3X, give or take a de minimis number of gamers. If 4e splits the existing audience, and it is doing so at this point opinion wise, it will do less well than 3x. The pie is finite and it is made up of increasingly grey gamers. If the thought is that 4e will "save" the hobby by bringing in nw blood that is a bigger fantasy than anything in any RPG.