I'm perfectly informed about the status of the 121 / 727 on demand world. Hell I'm doing it right now. Point it one of the nuts has to crack at some point, that is to say where the costs of paying people to do the job in a reasonable way (be it direct salary, days off, or otherwise) outweigh the costs of training / uncertainty over the long term.

As soon as someone starts offering the 40/20 rotation (off means off) I will probably be first in line.