I'd keep feats (if only because every other feat/PRC/whatever out of core uses them) mundane item and basic magic items (+x equipment, boosts to ability scores and saves, ect) and skills. Banning classes and non-standard magic items could be intresting, as would all but the most basic core spells (obviously heals, animal buffs, the stuff on the spell lists of the focused casters should stay). Otherwise the idea may be interesting.