Personally I think the band Anamanguchi would fit great with a pinball machine, and I've kind of just been drawing one out and writing up some rules occasionally in my free time. Not like I'm ever going to be able to do anything with it but I've just enjoyed doing it to pass the time.
But something I think Stern should seriously be producing right now? Ghostbusters. There's so much oppritunity to fill up the playfield with awesome things. Like not only could they find a way to use ghost catching as a play mechanic, but there are so many unique little items that would look great on a Ghostbusters pinball machine, like the Ecto-1, Slimer, the Stay-Puft man, and of course, the Ghostbusters themselves.