I would honestly be fine with a blank slab of silver that just reflected light sources. Working mirrors are notoriously hard for game developers to put in games, and that issue is extremely compounded in an MMO where players could put down multiple mirrors anywhere in an area. But we don't need fully functional mirrors to have great looking furnishings.

For example, there's an amazing looking vanity in Haukke Manor, but the mirror is broken. They can't give us the vanity, because they would have to put a working mirror on it, and mirrors are hard to implement. But who cares about that?! I don't need to see my character's reflection, I just want an awesome vanity in my house! Yes, it would look a little silly having a "mirror" that didn't have a reflection, but I would much rather have that then not have mirrors at all.