Well, one could go on and on and delve deeply into details that in the end are going to matter FAR less than the overall approach being taken. So, I have several basic assumptions about MY version of 5E.
Every version of D&D has its good and bad parts. While the oldest versions definitely suffer from not having over 30 years of game design incorporated into their workings the newest versions have DEFINITELY lost a secure grasp of elements that made D&D popular in the first place. Also, no one version of D&D is (or even could be) all things to all players. Accordingly, only a fool would dismiss any version of D&D out of hand or assume that the most recent version of rules or approach to any aspect of the game is always superior.
The next thing is that there must be the assumption that a new edition IS needed or desirable. It would be an exercise in stupidity to introduce yet another version of the game if it's only going to result in a further fracturing of the community. As a corollary to that, it seems adviseable to me to shoot for a version of the game that is somewhere between 1E/2E and 3E, leaning a bit closer to 3E.
5E will be no different than any other new version of D&D - some will love it, others will hate it REGARDLESS of what you actually do with it. The only thing then that you can do is pick the ONE person whose vision of changes seems to hold the most appeal to the widest audience and let them lead the way.
Simpler is better. Too much choice is as bad as too little choice. Fast character creation, rapid and easy learning of the essential rules of play, and simplicity of preparing and running the game for the DM are ESSENTIAL elements.
D&D is a game built upon character CLASSES - archetypes of fantasy fiction. Homogenization of character customization goes against that basic conceit.
This next bit may be more just MY opinion, but this is MY version of 5E not yours... It is a mistake to assume that so much of the fun of D&D lies in the "BUILD" of a given character as opposed to simply PLAYING that character in a variety of game situations. Character customization and optimization is fun and all, but it is NOT the be-all/end-all of the game. It is just ONE presently very OVER-emphasized aspect of it and I believe this is partly what has driven such a large portion of the potential player base to seek older versions of D&D if not other RPG's (including clones) altogether.
New and hip races, classes and abilities created from whole cloth are fine for supplements but the core rules should hew much closer to representing established fantasy rather than blazing new trails, again in aiming to appeal to the widest possible audience.
There are two areas of the game which dominate the rules - combat and magic. The magic system that is devised for the edition of the rules is inextricably intertwined with the rules for combat and vice versa. The older magic systems (actually from 3E on back) suffered from a need for too much arbitrary interpretation and implementation. 4E... well, let's just say it doesn't work for ME in that regard. I believe a better way is to be found somewhere in between.
And then there is TECHNOLOGY - and this may be the most important aspect. Since this is all pie-in-the-sky anyway I'm looking at the future. What I see RIGHT NOW is 3d TV coming to market as we speak, and a large and increasing desire to use laptops, cellphones, iPads, etc. to play the game. What I want to do with my version of 5E then is move the game to a 3D tv-represented game world. No more vinyl battlemats, resin dungeon walls, or heaps of carboard tiles. THIS version of D&D will have kitchen tabletop rules as a SECONDARY element. It will be designed and intended to be played (at least for exploration and combat aspects of the game) on a 3D TV interfacing with as wide a variety of controllers and devices as possible (thinking of Wii, Xbox/Kinect, as well as cellphone and iPad). So before it's even released it has to have worldbuilding tools - the virtual game table - built and ready to be used and improved by players.
There's more to it all than just the above, but my vision of the next version of the game should be apparant.