naw, it can turn quite opaqe. my only issue is it being too slow, or light degradation. but digital SLR's use the shutter for exposure dont they? i mean if the sensor turns on and off for the exposure then why is there a mirror to begin with? and yes this is only feasable for digital cameras cause it needs a current. theres not that many benefits, other then no parts ot wreck... but its just an intruing possibility.
oh and you remember the old 3D movies, where you had glasses with blue and red, then you had a film with overlapping blue and red images. well when you wore the glasses, the 'blue eye' would see one (blue) image, and the 'red eye' would see the other (red) image, giving a feeling of 3D. now we have LCD glasses where at any point in time, only one of the glasses is transparent while one is opaque. meaning, when the 'left image' is on, the left part of the glasses is trasparent, and the right opaque. then it switches to the left, and so forth so fast that you dont see it, and it ends up looking 3D. the cool thing about this now is that you can watch colour 3D movies.