The only thing I would be absolutely sure of would be to have different "power" mechanics for each type (Arcane, Divine, Martial, Psionic, etc). That was the biggest thing that turned me off to 4e.
There were a lot of issues with 3e, but I loved how there was such a play style difference between vancian casters, incarnum users, mundane characters (with combat feats feats), psionic characters, and Bo9S characters.
Other changes i would like:
I would also try and focus on a "realistic" (loaded term, i know) fantasy environment, rather than one based on combat equivalence.
First level characters would probably be more durable (less 1 hit kills) than 1e characters, but no where near the "already hero" status of 4e characters. I do like the minion idea though, as well as the tactical combat. Also risky combat is good, I like some of the ideas put forth in the "brutal 4e" modifications (don't have a link right now).
I would love to bring back the stronghold concepts, as well as the "estate management" ideas to go with it. A supplemental wargame to go with it would be fantastic (assuming they do a good job, like warhammer fantasy battle). It provides a nice change of pace to dungeon stomping, and it makes a lot of sense as far as campaign progression, it also adds additional carrots for the players to follow (for example: delve this dungeon to get control of a mithril mine to equip your infantry with).
Magical items would be more in the 1e/2e vein (HOLY




I FOUND A FLAMING SWORD!) rather than 3/3.5e style (stack more bonuses!! I even have magical underwear!) or 4e style (it is expected you need to have x amount of magical items at y level to get z bonuses in order maintain equivalence to the monsters... boring.)