I’m not sure if I like force ghosts being able to interact in the physical world at all. They COULD potentially wield lightsabers etc but it is clear they can only appear in moments of need as the Force wills (as Ben says to Luke before he rushes off to confront Vader, “I cannot interfere”) so maybe it’s no problem.
I suppose Qui-gon appearing to confront Vader and let Obi-wan escape would be a nice moment in many respects but it would all depend on execution.