I believe that Void Pillar does not need to cost 1 , for both flavor and balance reasons. Flavor-wise, no other pillars cost anything. Balance-wise, no one in his or her right mind would use Void Pillar as the sole win condition of his/her deck, since most decks in the PvP environment are either splashed, duo, trio, or rainbow.
Then why on earth would we introduce a card that hurts monos the most, if they're not even the most competitive right now?
Also, if I run a deck with half void pillars, I still stifle duos pretty effectively as well, because half the cards in their deck are now unusable.
To give people something to think about, just think about some of the games where somebody has dropped 2-3 devs/pests on turn 1/2, and how stifling it was. Now imagine that draws like that are now
virtually guaranteed.