The more I think about it, the more I'd like to see a 5th edition D&D that's a modular set of rules based around a core mechanic and core classes. Go ahead and give me two combat systems, one that's quick, easy, and doesn't require minis, and one that's got all the tactical options with 5' steps and rules for determining cover and AoOs. Give me two standard sets of spells, one that's nice and has minor consequences, and one that's hardcore and has deadly teleports and haste that ages people.

Heck, they could sell the "add-on rules" as $10, 50-page paperbacks. And the book could just say, "to use these rules, replace chapter X of the PHB with this book." Then they're making something that both players and DMs will buy, and they can make more segments of the market happy.