You don't need to be able to run 2 1080ps. For a game that wanted to allow dual-output multiplayer for, what, up to 8 players I guess, it could use whatever res it liked. 2 720p screens is less resolution than 1 1080p screen, for example.
I don't really see how many games this would be usefull in . It sounds like it would work with basket ball .... I fail to come up with another one where 4 players on each screen would work out well .
Dual screens is nice when its 2 people . I don't see it working with more than that unless you split the screens up in to 4s of course that would hardly be fair to the second group that isn't on a 50 inch hdtv or whatever