Man I know it would never happen, but I'd love to see a Donkey Kong Country pinball machine. You could have a series of moving barrel cannons that lead to a ball lock or something, a buddy system that allows you to pick any two DKC characters at any given time for unique perks, and of course David Wise could do the music. Man, I'd love to see what kind of music David Wise would write for a pinball machine!
Other themes I think would be cool would be Zelda, Metroid, Kirby, Portal, Pokemon (Not a Pokemon fan, but I do really enjoy Pokemon Pinball on GameBoy and it could be really popular with a lot of people), and Oregon Trail. 
