Write now, a software back update need a reboot, even for updating the backup software. I think it would be better if Active bank and Software bank update would be independant so we can put a firmware on a bank without reboot and only reboot when we want to change the active software bank or load the new firmware in RAM.
I think that would also be great for firmware test upgrade to be able to choose the active bank and be able to past from a firmware version to a other and do all our test without having to switch the SMs from a AP to another.