This is a very serious security concern, in my mind. I regularly type into the "wrong" window, due to (pick one) poorly designed UI or my stupidity.

This is mostly harmless in my solo environment, although one does have to be careful about things like .bash_history and websites that might actually be listening for keystrokes and sending them upstream. Having a team window seems like it would make this a greater risk.

On a different topic, I'm one of those people that can't stand pair programming and related--it destroys my ability to concentrate deeply on the problem in front of me.

Even with CoScreen you only share screens/windows when you want to. You can go online/offline with a tap of a button and in any case it only shares windows on a display you choose.