Mirror, Mirror: no. By extension, MU=no.
If they must rehash for the next movie, I'm still in the Doomsday Machine or Balance of Terror camp.
But to stay on topic, sort of, I agree that Mirror, Mirror doesn't a feature film make, and that adding MU to AU just feels too nerdy for general audiences to swallow, never mind giving fans one more thing to groan about.
I really liked the ENT In a Mirror, Darkly ep. I would love to see a CGI big screen appropriate version of TOS Defiant or even Enterprise pop out of 'whatever'. Yes, this is utter fanwank, and I don't think it's the forward motion the franchise needs.
Might as well hope for the 1701-A to pop with Shatner on screen for a five second cameo, if only to deliver his famous "Good morning, Captian" line to Pine. ROTFL.