I don't think it would work with the corebooks, for reasons stated above, unless one had absolutely Kick Ass art. And maybe some godlike lay-out and organization that makes people go "woah". As a very minor part of an example of the latter, putting the non-epic feats from the epic players handbook section, the non-psionic feats from the psionic section, etc., together with the feats from the players handbook section, so a player could have all available pc feats in one place would be nice. But I imagine someone could do that online too.
There might be a market for other 3.x stuff if someone (not me, btw) has the balls to say "well rules can't be IP so I can't be sued, right?" and puts out the rules of, say, Complete Arcane, etc., but with completely different fluff-text for everything that would otherwise be legally actionable. Witch instead of warlock, perhaps. This would be a hellish amount of work, imho. IANAL, I have no idea if this would work or what else would have to be done to make it work, and anyhow, just because it is technically legal doesn't mean you couldn't be sued into oblivion anyway.
Assuming Wotc/Hasbro does not sue the person/company into oblivion after that hellish amount of work (and remember, Hasbro has more money and better lawyers than you), people might be interested in picking up these works, simply because it will be harder and harder to find the hardcovers (only a finite number were made, and there is no indication that more will be made).