I like the idea, but Capcom is only getting good at character. A hypothetical MvC4 with custom assists may fall apart at the seams lol. They really ought to give better to assists to all characters though.
Yeah I've said before, fixed assists are intentional by game design, or even if not are a good idea on drawing the line for what is too crazy and can be game breaking. Especially in UMvC3, regular infinites would be even easier to create, which is not what they want; they want infinites to be exclusive to X-Factor. Makes sense, tie potentially big rewards on the scale of infinites to an actual resource you have to manage.