Pokemon is the only IP I can think of that would potentially get a large number of non-pinball players to get IC. All they'd have to do is let you catch Pokemon and have the ones you've caught saved to your account. It would be a cool feature and would definitely catch the attention of Pokemon fans.

Whether or not any of those players would continue using IC for other pins, I'm not so sure, but I'm sure a few would get hooked!

Not really sure how you can say Pokemon would be a horrible theme, translating it into pinball writes itself. Heck, there are already two official digital Pokemon Pinball games and they're pretty good. I say this as someone who doesn't really care for pinball games on the Game Boy or Pokemon in general.

It's a series about catching cool monsters in PokeBALLs. You could have a Dialed In style hologram and magnet setup where a Pokemon appears on the playfield, you shoot the ball at it, it gets stopped by the magnet, and an animation of the Pokemon getting sucked into the ball plays. Modes for training, battling, and evolving Pokemon. Getting all 8 gym badges to reach the wizard mode. Game buffs based on which Pokemon you currently have on your team. A difficult multiball mode where you have to defeat an organization of evil Pokemon trainers. Just a bunch of random ideas here, but the point is that there's a lot of stuff from the series that could be translated to pinball in cool ways.