The Ultimas were (mostly) wonderful, especially Ultima 7, but I don't think there's anything particularly valuable about the "IP".
It was really about Garriott exploring innovative ways in how to translate the tabletop RPG experience into a computer game. You don't need an Avatar or Britannia to pursue ideas like Ultima 4's virtue system or Ultima 7's interactivity.
Unfortunately, EA still holds the rights. The new mmo-ish game that Garriet made is one I have not really dived into yet