So apparently one suggested name for the planet, were it to be visually confirmed, is 'Nox'.
This is the Latin version of the Greek goddess Nyx, who is the goddess of the night.
This would be a clever name, given the planets suggested darkness. It's suggested to give back a fraction of the light which Pluto reflects, which is in turn tiny compared to the other planets. It's possibly 600 times fainter than Pluto.