Margaret Weis, Tracy Hickman and Don Perrin. Now that Dragonlance seems to have been shelved, I'd like to see them work in another of my favourite series.
Oh, if we're doing "late" writers, I'd love to see what H. Beam Piper, A. Bertram Chandler, Poul Anderson or James H. Schmitz might've done with a Star Trek novel. Anderson wrote a Conan novel in the late '70's, so it might've been possible. I'm pretty sure Marion Zimmer Bradley wrote some Trek fanfic back in the day. I'd LOVE to read that. (I've always thought Ann Crispin's Yesterday duology read like "Star Trek on Darkover".) Back to the living: Allen Steele would've done interesting things with Belle Terre, had he written one of the New Earth books.