Stuff like the traitor thing is always iffy. It COULD be super awesome. In a perfect world, it WOULD be awesome. In the real world, somebody'll muck it up. Would the 'spies' be known to each other?
On one hand, that'd give them a lot more angle to play with it. On the other, then if one person gets 'caught' they can probably get mindfucked into outing the ones they know. Which is all realistic and stuff, and one of the dangers even in real life of 'spies' knowing each other/etc.
Also you'd need to keep that on the downlow as a player OOC. And it feels like it could breed this weird paranoia in-game (which, admittedly, could be fun), but with all the OOCness that goes on on games, keeping those kind of things OOCly a secret is pretty hard. The minute you got 'oocly outed', I feel like it'd just be a matter of time before that 'somehow' turned into ICly outed.
I dunno, just my random thoughts as I consider it a bit. A lot of fun. Potentially a lot of mess.
Onto servus-- Will they have powers, a-la ghouls? And TBH I'm with you on the humans, like I said, not my thing, but I know it is for some people. Having the servus is probably good enough.
And yeah, the powers thing. As long as all the options are at least 'kind of neat', I wouldn't even worry about it too much. I've been playing Guild Wars 2 lately, and even there, half the traits my class gets are clearly worse than the other options.
Yeah, I'm sure some 'meta' build of murdervamp will arise, but eh. It's a MU for RP, and with the politics/other powers/etc, should be ways around dealing with that, anyways.