I guess it goes back to the early 90's when REI had a sleep system that was supposed to let you get your arms out and use your hands while still in the bag. I don't think it was very successful. They were aimed at climbers but I never met a climber who had one or thought it was worth having.
You mean something like this?
I got it back in ~'88 for a climbing trip to AK.
Still have it and this (new to me) bikepacking thing bought it back out. It isn't as light as the more modern stuff, but it is pretty light considering it is ~22 years old...
oh, and it has 4 zipper heads...
g