The keyboard should use multi-touch to allow uppercase letters to be quickly typed. That is, holding the caps button down with one finger should allow typing uppercase letters with the other fingers.
This can work with the existing design, if another button is pressed while holding down the caps key it should cancel the caps-lock when the user lets go of the caps button. If no other button is pressed before the user lets go, it should work as currently designed and enable the caps lock.
Adding this feature allows more intuitive input, allowing users to use this in the same manner as a shift button on a physical keyboard.