They are not getting a new coaster. It's just a relocation and retheme of the kiddie coaster they already have.
Well, the park got their first new roller coaster in 20 years. So, that's a start. The last
new roller coaster the park received was in 1999. They're screwed.
In reality, the park is very isolated as a tourist attraction. Off the beaten Grand Rapids/Grand Haven path (which is the main tourism draw), visitors struck me as being primarily interested in the water park section, with roller coasters an afterthought. It truly is a bottom-tier park that has
just enough relevance to draw a crowd and profit.
It's important to recognize regional markets and anchor cities for parks; which again, Michigan's Adventure really has none. Chicago has Six Flags, Detroit is Cedar Point's
number one city. And with only Grand Rapids and East Lansing you're nearby cities, that barely gives you a core population of 300,000. South Bend, one of the next nearest cities, is about equidistant to SFGA.
Population demographics play heavily into decisions that are made by park chains on which parks receive priority projects. And, as is evident, Michigan's Adventure just hasn't been it.
That all being the case
A great, major roller coaster that I could see a good fit would be a Gerstlauer Infinity Coaster, a la Hangtime at Knott's. Great compact footprint, meets capacity draw well for the park, and would give it a novel advertising edge to the market (steepest drop in the midwest?). The park is very U shaped in it's design right now, and it would be great to fit this new coaster behind Wolverine Wildcat, connecting the pathway back towards Thunderhawk to complete the loop: