Well, that's my thought on Combat Casting. I just re-read it as close-combat casting.
So you're suggesting that, without feats, the casters have no options other than to eat the AoO when threatened, and Combat Casting only allows them to cast touch spells up close?
Another option I like would be to only have a spell provoke if it has a somatic component and/or takes longer than a full-round action to cast. This would make Still Spell a more attractive feat for a caster. It allows you to cast in combat at the cost of a feat and a higher-level spell slot. Note that in my house rules, everyone casts spontaneously and metamagic feats don't increase the casting time.
Given those two house rules, do you think Still Spell is enough to justify what you suggested?