What if you got rid of the one thing that I think has really distorted the character creation process in 4E--the ability score modifiers to attack rolls? Score synergy becomes more an extra than an essential if it's only modifying damage rolls and rider effects.
On 5E in general, I like Jack Daniel's idea (it reminds me of one I proposed a couple years back

) and agree with you on what the game probably should be. I think 3E made a mistake by building up the rules complexity and system mastery elements to such a degree that D&D became virtually unplayable as a 'pick up game', and while 4E's backed off from that to a large extent, it's still got problems. Essentials is pretty good--clean up some of the details, remove the need for system mastery and build focus from the core game, and make the grid optional, and I think we'd be in pretty good shape for a baseline that could then be built off of for more complex games for those who want it.
One thing that I think makes 4E viable as a baseline for this kind of modular, multi-level design is the emphasis on keeping character sheets and monster writeups so self-contained. Move the 'forced movement' powers into
'C&T', put stuff that requires more careful DM adjudication into 'AD&D', put skill powers in 'S&P' and elaborate magic into 'Sp&M' and so forth, and I think you'd have a good setup.
The danger, of course, is the same thing that TSR risked in 2E's days--excessive division of the fanbase, especially with the insatiable demands for 'support'. However, I think that the division is a
fait accompli, and WotC is better off trying to make material that's reasonably accessible and modifiable for all facets of the audience. Based on his recent L&L columns, Mearls seems to get this.