I'd want a group of the Best of the Best in D&D writers (mostly rules-wise, since the core rules are just that, rules), but not limited to:
Monte Cook
Mike Mearls
Skip Williams
Sean Reynolds
With the following in an advisory role for style and flavor:
Ed Greenwood
Gary Gygax
Show them 3.5, and say "This was excellent, make it even better."
Remember that this is D&D, if you change it too much it will be D&D in name only. Claiming "No Sacred Cows" is a fallacy, if it was a percentile based classless skill-based game with an open-ended non-vancian spell system that only uses d12's (for hyperbole to make a point) it's not going to be D&D anymore, no matter what you call it. It might even be an excellent game, but it's just not going to be D&D.
Preferably, make the Forgotten Realms the default setting instead of Greyhawk, put Psionics in the core (at least Wild Talent rules in the DMG as an option, preferably a Psionic class and full psionic rules), and liberally borrow some good ideas from Iron Heroes (the Man At Arms becomes the new Fighter, IH Thief strongly inspires 4e Rogue) Arcana Evolved (generic spells like Ability Boost and Energy Bolt instead of Cat's Grace and Lightning Bolt), and d20 Modern & Unearthed Arcana (Action Points, Class Defense Bonus, Reputation Bonus).
Add a spontaneous divine caster to the core rules (Likely to be a derivation of Favored Soul, but lose the wings and replace them with another ability). Make Paladin a Prestige Class, the same class as Blackguard except the abilities depend on alignment.
