I really would like the ULTRA attacks to work off of combo meter. You land enough consecutive strikes you are granted a character specific ultra. I am not a fan of a little ball flying around open to anyone.
Agreed. The Final Smashes would have to be re-balanced for that to happen though. I think that a cool Smash-ey way to pull that off would be to have the crowd start chanting after you meet the pre-requisites for the power-up. The powered up state would last about 20 seconds and have the following two benefits:
1. Your defense increases and your moves hit harder.
2. You have access to the Final Smash. The catch is that its power decreases the longer you go without using it. This would add an element of strategy as players would have to choose between being buffed or going all out with the Final Smash.