Ooh, are we coming up with ideas for upcoming Stern pinball titles just for giggles? I don't think that anything that I personally like is very popular, so I am going to go with more practical guesses - mostly sticking to Stern's bread and butter of male oriented nostalgic properties, blockbuster movies, and old rock and roll artists.
1. ET - a nostalgic blockbuster movie that I am surprised hasn't gotten the pinball treatment yet.
2. Pokemon / Mario - you know, at this point, I assume that there are extenuating circumstances to why no one has made a modern pinball with either of these franchises.
3. Tesla - weird, I know, but car-brand pinball games aren't unheard of, and Tesla fanatics tend to have a lot of disposable income as well as a high brand devotion.
4. Saw - This is the economic pick. The Saw franchise is kind of trashy, so I expect that the license would be super cheap to pick up, and all of the death traps could inspire some great playfield toys.
5. Dr Seuss - I don't think I need to elaborate on this pick. It would obviously be based exclusively on the celebrated live action adaptations like that one that features Mike Myers in a creepy cat costume.