I think we all agree that the line input idea is regrettably dead. Brian's findings sort of put the nail in the coffin, which is a shame because I really like the idea.
BTW I would just like to note that it is very unsurprising that the key data defeating this FANTASTIC idea came from Brian :)
On another note, I think we could have easily handled this stack trace scenario. It's manually triggered so the overhead to the protocol is minimal. It just pointed out that we really don't know what can go to STDOUT and when.