If it builds on Enterprise's "In a Mirror Darkly," it could be good. But I remember a Mirror Universe storyline from DC comics circa 1985 or so, that took place chronologically between TSFS and TVH. It kinda sucked.
Personally, before Star Trek ID, I remember the rumors that Cumberbatch was actually playing Gary Mitchell, and was actually kind of excited about it. Would be cool if they actually go through with that.