The only major character of the original trilogy who is expected to have a major role in Star Wars Episode IX at this point is Chewbacca.
If Episode IX feels a need to connect itself to the original trilogy the way the previous films have with the characters from those films, bringing in Lando would be one way to do it.
Mark Hamill might appear as a Force Ghost or a disembodied voice, but he won’t be a major character in the story.
The idea of seeing Lando return certainly makes some sense.