I was on my way to creating something similar. The sweet spot thread got me thinking.
My idea was to stop numerical advancement at level 10 (for PC not for monsters). HD, spells, attack bonus, saves. Also max skill ranks top out at 10 and are no higher than character level (It will become clear why later.)
Eliminate full round actions. Things instead break down into, standard, move, free and possibly swift. IMO immediate actions clutter things, also because they should be involuntary or reflexive. Full round action spells with a duration would be standard + concentration, instantaneaous would be 1 level higher than normal.
Eliminate AoO's for movement. This would aid melee types. Additionally I had considered only allowing fighters iterative attacks. That look like this. But I'm not so sure.
+1
+2
+3
+4
+5
+6/+2
+7/+4
+8/+6
+9/+8
+10/+10
Touch attacks would be handled like normal attacks.
AC and skill DC's stop at 30. Additionally apposed rolls are handled differently.
Ability scores top out at 24 plus any size modifiers.
After levels 1-10 I am trying to figure out how to give cookies so to speak.
Levels 1-10 characters are treated as heroic.
levels 11-15 they are treated as super-heroic.
levels 16-20 they are treated as legendary.
above 20 they are godlike, or demigodlike.
While skill DC's top out at 30 their meaning changes at super-heroic, legendary, and godlike.
DC's for actions go down for PC's that achieve super-hero status and greater.
Move silently: Heroic
DC: 10 moving cautiously
DC: 15 moving quietly.
DC: 20 moving steathily
DC: 25 very stealthily
DC: 30 Moving silently (no sound at all, beating this means DC:30 Super heroic listen check = echo location)