Touch screen would not be very good. You need the tactile feedback from the keys. It is like TV remotes. The all touch screen ones suck, you need hard buttons, so you know what button your finger is on. And feeling the button depress actually gives you feedback that something should have happened.
true touching glass or transparant plastic or whatever gives off no feed back
but someone posted a yahoo clip by the wii-mote guy doing a force feed back thingie and he used this pen device on a touch screen ... i thought it would break tbh
so modify that to 10 force feed back finger tips and you could have the optional ffb glove
myself id prefer an illumination of keys hit
i dont know the sensitivity of touch screen as ive only ever used the one in hmv (when its not BSOD) but iir you could rest on the home keys without asdfjkl; coming up all the time
all you would lack would be the f and j ridges designed to let you find the home keys with ease (a tacky overlay perhaps?)
edit:
i looked at the pc pants
who in their right mind would type on their crotch?
i know i have my kb on my knees but thats just bloody rediculous