That's oddly specific. Unless we get some "set minions attack to 2" cards or "swap attack with this minion (which has 2 attack)" I don't see a reason to play this.
edit: "or less" was added. In that case it's alright. Decent token killer and get's around Divine Shield, doesn't trigger Imp Gang Boss, Acolyte of Pain etc Not sure if you would want to run such a dedicated specific removal tho, since most of the time you get more value out of flat AoEs like Holy Nova.
I think there have been many hints that cabal shadow priest will be nerfed, and this is another one.
Wait, it says "all" minions? This card is bad for priest, it kills the 2/4 taunt, the card draw 1 mana minion, etc. People, this card is terrible, don't you notice that it also kills all of your minions?
Edit: for everyone saying this is a "zoo/agro stopper", note that most minions of such decks have 3 attack or more. It is priest who's early game consists of 2 attack or less minions (cho, north shire cleric, wyrmrest agent, 2/3 1 mana dragon).
This is what we get instead of Lightbomb. Wow. If I want to get rid of a 2 atk minion, I will use Cabal to steal it... Why destroy crappy minions? If we still had Shrinkmeister, it might have been sort of useful to kill Ysera or Malygos. But now...