I personally don't like the idea of using the UART itself to initiate an ISP procedure. I don't think a break should initiate ISP nor do I think some special string of characters should initiate ISP. That just seems too dangerous to me in terms of potentially being able to accidentally enter ISP mode.
Everything is a trade-off. With NoTouch you can set it up to enter ISP based on a UART string or a pin held down. Of course, NoTouch is my baby, but the below apply to any means.
UART string: you have a slight risk (I have yet to see it happen) for "QwErTy" coming down the pipe, but you get the advantage of "connect the cable and go" which means the customer can do the update.
Held pin: you have no risk, but need a mechanical means which probably spell "send technician" in order to activate ISP.

Erik