Realistically, Cedar Fair is going to want to go with someone who's reliable and has a pretty good track record. I want to rule out gerstlauer from this park just because I feel like they're coasters are geared toward smaller tier CF parks. For example, a Gerstlauer at Worlds of Fun would be more realistic than them getting a B&M at this point.
I know everybody's thinking Mack but they're pretty expensive because they manufacture everything overseas. I don't think Cedar Fair would want to invest another 20 million dollar coaster at Kings Island after they poured all that money out for a giga. Much like how we got an affordable GCI after Banshee, I think we'll be getting an RMC to save some money.
This also fits in with my theory that each major section the park get something in a specific order. Xbase/Area 72 got Firehawk in 2007, Rivertown got Diamondbackback in 2009, Action Zone got Banshee in 2014, Rivertown got Mystic Timbers in 2017, and now Area 72 will be getting Orion in 2020. If you follow this logic, Action Zone is the next section to get a coaster.
If KI could fit a roller coaster in within the train ride with Mystic Timbers, they could make something work for Action Zone.