Well this could have potential, lets say the limit to how high you can charge is 2x...but by the time you get to 2x your ki reserve is at 1/8, not to mention that your ki is burning so fast you have only a few seconds to act on your power, you don't have much time to act so basically charging up that high would be if you wanted to get in a big melee hit on someone.
To make it work with buttons you would have it so that when you tap turbo once you go 1.25 and then if you hit it again it goes up a bit (also having ki burn a bit faster) if you let up and hit again then your turbo goes off, but if you continue holding the second time, then your turbo goes up
Now I have no idea what you guys are talking about with the charging and turbo at the same time (haven't played in a while) but aside from that, this sounds like it would work well