There should be a simple warrior class.
But that should be the barbarian.
Thematically, sure.
But you would have to rewrite rage and reckless attack.
Rage: you reduce all damage by X
Reckless attack: you gain a permanent +3 to attack and a permanent -3 to AC.
There should be a simple expert class as well.
Scholar: when you roll a skill check, your minimum bonus is equal to your Scholar level. (I.e. at level 10, all skills have a +10 modifier).
Adds xd4 damage to all attacks and you're set.
There should be a simple priest class as well.
Medic with a much bigger pool of lay on hands would be quite simple. Add a limit to how much you can heal per turn and toss on a self-sanctuary and your golden.
There should be a simple mage class as well.
Hmm... Maybe:
You can cast spells at-will. You cast them at the spell level according to the chart (scaling slower than a wizard).
You do not need to make concentration checks for spells cast this way, though may sill only have one at a time.
1: magic missile, burning hands
2: certain rituals (which are at-will).
3: feather fall
4: feat
5: all spells are cast at level 2
You learn certain utility spells you can cast at will (water breathing, darkvision, fly)
...
11: all spells are cast at level 3. You learn fireball.