With conventional PSR, I think the goal is to power off the link between the system framebuffer and the display controller and potentially power down the system framebuffer and GPU too. This may not be beneficial unless it can be left off long enough, and there may be substantial latency to fire it all back up. You do it around sleep modes where you are expecting a good long pause.

Targeting 1 Hz sounds like actually planning to clock down the link and the system framebuffer so they can run sustain low bandwidth in a more steady state fashion. Presumably you also want to clock down any app and GPU work to not waste time rendering screens nobody will see. This seems just as challenging, i.e. having a "sync to vblank" that can adapt all the way down to 1 Hz?