Considering faces have been turned into straight-lined vector graphics rather than just pixels on the face, I’d say this is definitely within the realm of possibility.
Face changes definitely should only apply to very specific and/or short-term circumstances (taking damage, being too hot/cold, death, etc.), and those expressions should not be options for customization. I think that last point is very important so that there is a clear line between expressions happening from stimuli, and just the normal, blinkless stare the character normally gives.
(Speaking of not blinking, can we also please get more idle animations such as blinking to feel more alive?)