Yeah, i see this card has become very popular, i've even heard its the best card of the expansion.
I've also heard, and even thought so myself, that it cant be stopped, but yesterday found out that's not the case at all.
I thought locks wouldnt work unless you immediately locked both (with Auckes or NG stratagem+lock), but all you need is to lock the rightmost ethereal, and the left one wont transform the locked one because its still a demon.
Locks were pretty much neglected before this expansion, and with veil, i thought they would become even less popular. Maybe its the Ethereal threat that will cause a lock resurgence...
Yesterday i also found another (NG exclusive) counter to ethereals. All you need is play an enforcer, the opponent plays ethereal, you play a mage infiltrator between them (3dmg to each) and finish both with your 2 charges.
And finally, there's row punishment like lacerate, Lambert Swordmaster, Regis - all these allow you to ignore the ethereal swarm and punish later. Also, the new SK warriors with their Hemdall+GS punishes this really well.