Show only the current space

Fantasktik could be a terrific solution to the one big problem with Spaces: There's no way to keep your Spaces separate. How about an option to "Show only windows in the current space?" For apps that have no windows open, you could keep track of the last space they appeared in.

I know that Spaces APIs are limited, but I think apps like HyperSpaces and Warp have found ways around that...