Make it pillars only. It just feels right like that.
Hm, are you sure? As a baseline a well designed card should have 3 strategies to be considered viable.
The only time players generally want to target pillars is if they have 1) Earthquake or 2) Repeatable PC and no other permanents to deal with.
One option is card-specific/situational while the other is expensive and unlikely to happen until mid to late game.
The strategies I see are:
1) Combo with the above denial cards.
2) Protect against the above denial cards.
I think limiting it to pillars is too much. Most players usually don't use more than 4-6 PC cards a deck, so this is probably still worse than Quantum Pillar even if your opponent is dedicated to blowing up your permanents and pillars. (Note that Earthquake only counts as 1 instance of PC, based on Salvager.)