Great - but I think it could go a little further to work properly.
In addition to the musculature of the face, changes would need to be made to the underlying bones. Bone would need to be removed in multiple places to allow for ratio changes between the various facial feature to allow for expansion or compression. In these joints would be placed either implanted servos (bad for lots of reasons) or tissue that could be caused to swell or contract as needed. This would allow for dramatic changes in appearance but would have the side effect of reducing the structural integrity of the face.
Another side effect of this is the facedancer loses their original face. Their resting face would be an odd one - contracted with with features a bit too close to be natural. So, they would always normally be acting.