The design is technically not Mother Talzin, actually, if you look at some of the small details. For example, the Nightsister has pigtails and a lightsaber, and is similar to a composite design from a few years ago which appeared in (amongst other places) the WOTC Miniatures game. It wouldn't stun me if it was "good enough," like how the Death Star Droid was C-3PO for one of my neighbors. Drove me bonkers.

Given the fact that this character design isn't someone specific I have to wonder if Hasbro isn't doing Mother Talzin yet or just not doing her for some other bizarre reason which we mere mortals can't fathom. Because if ever there was a better time to do it... I can't think of one.