There are several things I would like to see done by WotC.
A lot of it would be updating and revising old material. Course, they sold off the licenses for a lot of the old stuff.
Releasing different limited editions of the core books woud be a way to keep producing more product without spending a lot on R&D. Like releasing the various versions of the Monster Manuals in one compiled uber-book. Then do a couple LE leather bound editions. Maybe a triple combo edition of the core rules.
I would like to see a book on Cohorts, Companions, and Familiars. Basicly a book that deals with NPCs and all the supporting characters. It would probably have a lot of fluff, but I can think of some crunchy stuff to make it worth while.
I really don't have to much against fluff in rule books as long as it is entertaining fluff. Most fluff in the current books is just presented in a trivial manner that becomes irritating. Fluff presented by way of examples and story-telling is much more interesting to read.
But I think it really comes down to WotC needs to start making adventure modules again. Not whimpy modules either. Big modules that take like a year to complete. Unfortunately, I think the focus on minitures has killed a lot of the creativity at WotC. Hence, modules that encourage good role-playing guidance are hard to find.