Nothing completely hypothetical either, but matches that could happen sometime in the future that I would pay money to see (if I ever paid money to watch matches). I'll start:
Bill Cooper vs
As you can see, these guys who both are around the 170 pound range have a common opponent in Jeff Monson. They both could be described as grappling prodigies with very exciting styles. Cooper has the edge in experience, he's been competing probably twice as long , but Gunner got so good so fast. Hard to call this match, but it would definitely be fun to watch.
Who do you got?
Who do you want to see competing?