I want them to take the lessons learned in the last few monster manuals about how to present monsters, and phrase monster special abilities, for maximum fun.
I then want them to insert template-like rules for how to take one of these stripped down monsters and put the fearsome back in; for instance, present vrock as very stripped down, suitable-for-bruiser-use monsters... and then present their out-of-combat panoply separately, allowing both ease of use in play and thematic place. Hell, if they're greedy, they could publish the ecology/culture notes and these out-of-combat templates in a separate book, forcing you to pay again for the same creature you've already bought.
I want them to take the granular nature of Saga Edition skills/feats/classes and port them into D&D. They could have a nice home here.
I want them to, as others have said, make magic items *really* magic, and call mere enhancers by some other name (expand the role of masterwork!).
Then I want them to introduce a system of "boons" under the umbrella of the treasure system, putting prices on minor, point-buy-like expansions of personal power. This would let someone who really should have +2 sneak, because of X Y Z, get it anyway, but not require it for characters for whom just getting set up is more important.
I want big ritual-y magic to be big and ritual-y.
I want a LOT of sidebars. :-D