The 1991 HCIL Video Reports contains a demo of playpen. Touchscreen keyboards, a series of evaluations Touchscreen keyboards become attractive when only occasional data entry is needed. Several experiments refines our designs. We were able to design a 3 inch wide keyboard and demonstrate 20 wpm for experienced users and 10 wpm for novices. You can use speed and direction of the movement too.
Old touchscreens tend to be unstable and to loose their calibration.
Remember that some gestures unused by mouse applications can be more natural with a touchscreen, e.g., rotating the hands of a watch feels more natural with a touchscreen than a mouse. You can order the 1991 HCIL Video Reports who contains mainly examples of touchscreen applications.