As much as I'd like to see a third Black Knight or High Speed, I think we've reached the critical tipping point in pinball where it'd be best to just come up with something entirely new. I think the market can handle it. Besides, a 3rd black knight or high speed or firepower will be so heavily compared to the games before it, it'd be tough to please people with everyone wearing rose tinted nostalgia glasses.
Either way any unlicensed theme is good in my book. Especially if it's coming from Ritchie.