I had an idea earlier; what if you took normal DnD, and then hacked away all HD after 6th level?
"You are talking about e6, you idiot." I hear you all cry, but that isn't what I'm saying; what I'm saying is more on the level of:
-You level as normal; however, after 6th level, you no longer gain BAB, Skill points, and Base Save progressions.
-All "fiddly bits" are capped at what you could get as a 6th level character using RAI; so you would be limited to 3rd level spells, 3rd level powers, and so on and so forth.
-You would still be getting your bonus HP from Constitution and levels; however, you lose the amount you would roll for beyond 6th level.
-You still get feats and such as normal.
So, how would this change things?