If it is 75 times further away than Pluto, it is hardly in the neighborhood of the known Kuiper Belt Objects. Pluto's average distance is 39.482 astronomical units from the sun; Eris' is 67.668 astronomical units out and at last report was the furthest out object in the solar system that has been actually seen.
When Percival Lowell was hunting for a planet beyond Neptune it was called Planet X. Planet Nine could be called Planet IX.