while I can see the use in this (i only use my trusty thumbs as well) I can't see disabling the stylus keyboard going well. maybe if you could remove the stylus keyboard but map the thumb keyboard back to its entry. If you JUST removed the stylus keyboard without remapping back to the thumb keyboard, all those times that the stylus keyboard came up would just be empty clicks.

Not sure how hard this would be to do. I am assuming its getting knee deep in hacking the OS.