It seemed when I played that the demo required you to press the attack/charge button while at the same time requiring you to press a direction, either by letting go of the direction and pressing it again or by moving from a standstill. I thought of the run trigger in games like Super Mario Bros., where you can start running from a walk by simply holding the run button. I thought that would be much easier and more intuitive compared to the current trigger to start the charge in the demo. Stopping the charge doesn't have to be done this way if you want the charge to function as something other than a generic run.
I don't mind if you would lose momentum when you aren't actively increasing or maintaining it. (walk - maintain, dive - increase)
With regard to the speed cap, I'm not really sure what you mean, but I'm thinking you might mean something similar to high-level Super Mario 64 or Dustforce play (neither of which I can perform). Actually, this franchise(?) reminds me (favorably) a lot of Super Mario 64 in terms of movement.