That's a pretty big change there!! It would change the whole dynamics of the game if you could charge and move freely. If would also screw Ki blasts.
Or, are you talking very slow movement, so you couldn't fly all over the place charging your final flash, but could charge an attack at the edge of a corner, then slink around and blast it? That would also be interesting to consider.
I think the more powerful attacks like Spirit Bomb, Final Flash, etc, would be better left so you couldn't move.
Moving while charging a Gallit Gun or Kamehameha is one thing but imagine having a Goku char wandering around with a charging Spirit Bomb in his hands, he would become a lot more dangerous. I wont even go into FF, those huge attacks might be better left with their weakenesses intact.