Skepticism is understandable for the reasons you say, but the Demira incident is instructive: There were multiple hints her attackers were impostors, first and foremost being that the supposed assassination failed. Only Aes Sedai arrogance and condescension makes it plausible that THEY fell for it. "Most of her fellows can instantly heal her, but let's just leave her to bleed out here.... " There's also the long standing Aiel reverence and subservience toward Aes Sedai. And, of course, the fact we knew Rand wasn't sending out Aiel hit squads, let alone against Aes Sedai. There's precedent for such a masquerade, but the incident at the end of ToM is nothing like the one from LoC, so I don't see much similarity between them. I view it the other way: I don't rule out the possibility they aren't Aiel, but think it's a long shot, and if they are Sanderson better have a solid explanation without introducing large, complex and NEW concepts in the tail end of the series, or it will be very cheap.