John Ordover has said on occasion that a Star Wars
crossover was considered in the mid-90s. Pocket and Bantam would each have done a book, telling the story from different perspectives. But it would have been an unofficial, character-obscured crossover, like the Marvel/DC Invaders/Freedom Fighters
crossover in 1977.
DC Comics proposed to Paramount a Star Trek
/Superman crossover in the early 90s.
There were rumors of other Trek
/Marvel crossovers in the wake of Star Trek
. I remember hearing about a Voyager
/Dark Phoenix story, but at the span of ten years I don't remember any more than that.