I think the theme has to be cool, but definitely not a requirement that it's a licensed theme. I actually think it's kind of lame having all the licensed themes. It's just not creative. It just seems like when you do licensed themes you kind of shoe horn the pinball part in. There are so many options that I would take over another movie / band theme. Anything mythological would be cool, zombies, end of the world, Roman civilization. I mean, really anything. But I just think licensed themes sell better because it's known, with replicatable sales.
That being said I really want a GOTG or SW as my next pin, lol, hypocrite.