Basically, I think it would be nice to see a system (Flash/JS?) that would permit the creation of new maps. And, of course, maybe there could be a way for maps that are created to be reviewed and judged before being publically released.
However, it could also be a feature that is accessible with the premium membership. Maybe custom maps can only be played if the game is started by someone with a premium membership. It would limit who can make the maps and who can use them (and may be another incentive for paid users).
I don't know if its really needed, but I think that it would be an interesting addition to this already fun site.
Priority: 2