Spichora, sorry but your theory is pointless. I don't know if he will turn out be a traitor, and a traitor for WHO, but one thing is sure, the base on which you're building this supposed "treason" is just a violent butchering of the character, supposing reasons that are completely out of character. Completely.
After the Purge clearly his feelings changed, but just in line with his brethren in Silvermoon, that were always distrustful of the Alliance and of the Kirin Tor.
But before this damn purge, Aethas simply didn't had any reason for hate the High Elves. Even if the Silver Covenant had grudge and despised the Blood Elves and so the Sunreavers, he was the kind of guy that grin and bear it, make the best of a bad situation, keep a stiff upper lip, suck it up; he just wanted the blood elves to have their right place in Dalaran and do it with the best relationship possible with the Kirin Tor, not become the big boss of Dalaran, he was more than happy and proud of his place in the Council. He wouldn't made ANYTHING so stupid that could damage the relationship he was so desperatily mending with the Kirin Tor.
As i said, i personally find the whole treasoning argument a bullshit, but, looking at it more objective...it is not impossible that could happens, but absolutely not with such motivations. It doesn't make sense. At all.
You're also make too much speculation on Thalen. What's strange that he volunteered himself for Theramore? He was a spy. Spies need to be on the field for do their, well, spies's work.