It has to be in Jackson County. It's the only metro Missouri county with enough residents to financially support building a new stadium, or even maintaining the existing one. The only other is Johnson County, Kansas, and that defeats the purpose of a downtown stadium.
I agree with GRID that the stadium needs to be on the edge of downtown because there will be parking lots. The majority of park visitors will arrive by motor vehicle -- not a streetcar -- simply because the majority of fans live in the suburbs.
I'm against the stadium anywhere inside the downtown loop. So the East Village is out for me. I think the East Village should be developed with several blocks of mixed-use development. That would be the healthiest use of the East Village long-term. I imagine at some point at least one streetcar line running through the East Village-- probably 12th Street. Even if it ended around Kansas City University, a streetcar line would spur development of Paseo West into a future mixed-use neighborhood again.
I feel that same about the North Loop parcel. It should be development for year-round active mixed-use.
I am willing to entertain the riverfront. I think you could build it out with mixed-use buildings and a baseball stadium if one could convince the railroads to reroute some track, and give up some land for the stadium. I think a stadium could be squeezed in.
Red lines are rerouted rail lines added to existing right-of-way. Green areas are new development parcels created by moving rail lines south.