Wanted to post Hellpop's lineups in the new thread for reference. The fourth person in the second wave would be a challenge - Torgo would be great, but getting the rights would be a pain. (Doing a Mike in Torgo Costume figure - that could work).
For future box sets, there's the forgotten robots Cambot and Magic Voice. And the characters from the Sci-Fi years - Pearl Forrester, Brain Guy the Observer, Professor Bobo. And the more obscure characters, like Mike dressed up as Jack Perkins, or the Devil Dogs, or Dr. Forrester's original partner, Dr. Erhardt.
What about accessories? What about a free-standing silhouette of the bots in the theater? Maybe Joel can come with the Movie Sign button? Dr. Forrester with a toxic movie reel?
And why stop at Minimates? Who wouldn't want a MST3K planet logo bank? Or banks of any of the bots? Satellite of Love-shaped ice cubes from the MST3K ice tray? Gypsy oven mitt? Tom Servo gumball machine?