The IAE has it on the vote for P3 and P4's names, but I think they'll veto it if it wins (they've not actually approved vote winners on previous such stunts). The hypothetical planet Vulcan was disproved by general relativity, but the term is still used as a classification for asteroids with an aphelion inside Mercury's. I think Styx, Acheron, or Phlegethon are pretty much guaranteed to get the final approval no matter what the vote comes out, since a planet's moons are usually named on some theme.
Vulcan seems more appropriate to replace Venus which is not happening or one of those planets in another solar system that is too close to their star. It doesn't make sense for it to be at the edge of the solar system. Vulcan is supposed to be a hot lifeless rock not a cold lifeless rock. Even in Star Trek, Vulcan is a hot planet. A more acceptable name for this moon is Andor.