I said before that I kind of want it to be like magic items...here's what I meant by that:
Each ability you have should have a "slot."
Going back to my "noncombat roles" observation, there are basically four slots in any point-based resolution system: damage, make attacks better, heal, or make defenses better.
That's four slots.
Each class could fill those four slots, and use unique mehcanics to do each thing. Rogues damage with sneak attacks, make attacks better with disabling strikes, heal by inspiring with slick moves, and make defenses better by granting stealth. Fighters deal damage with melee attacks, make attacks better with taunts to the enemy, heal by gaining temporary hit points, and make defenses better by protecting their allies. Et cetra.
This makes some solid differences between the class abilities. A rogue doesn't play like a fighter, and they have different capabilities against different challenges. Those slots define how you interact in combat.
As you level up, you gain more options for these four slots, but these four abilities are always "equipped." So your fighter might gain a command that heals and also lets you make a free saving throw, but your rogue would gain a stylish stunt that could move you around after healing you. This would be kind of similar to the 4e powers system, but would be loyal to each "slot."
How 4e does magic items is that each item has a slot: waist items improve health, foot items improve mobility, etc. Each slot has a corresponding bonus that is narrow and flavorful. The different items you can equip in those slots are variations on that theme.
So my character has four abilities. He can customize those to a certain extent when he gains a level or spends a feat, but those four abilities are my character's core.
Everything else is gravy.
That's very rough, but that's kind of how I would envision an ideal D&D system. Unique, class-specific abilities that use different mechanics depending on the class, but also that are streamlined into a few over-reaching, defining characteristics so that you don't have this unwieldy deck of 10 different powers to use at any given moment.