Being able to have shared units in UMS would probably make gaming curve like bounds did. (Actually, I would like to see a team ums in a bound, you then could have more intricate obstacles if people could work together properly.)
Hmm... I wonder if we ever were to get Team Ums so there can be shared units and independant units in the game...
Oooh... what if non-allies shared a unit... now that would be interesting...