There is a sense in which it doesn't matter what I think - I am not in a position to be a Stern customer.

I suspect that band-themed games would sell well. Some high profile remakes could work.

Classic themes such as card, pool, car and so on are always worth revisiting.

What about themes based on a country? Australia - notable landmarks such as Ayers Rock, Sydney Opera House, Sydney Harbour Bridge, etc could lend themselves well to a pinball theme.