The standby generator requirement on 737 is met by keeping the APU running. I'm pretty sure we will be required to keep APU running until back in non-ETOPS environment i.e. 60 minutes from ETOPS alternate. Once we demonstrate the ability and reliability for a period of time, we may be able to petition the FAA to waive that restriction. That's why Alaska doesn't fly with APU on.

I could totally see us turning the APU off before taxi and keeping it off until ETOPS entry, and then have APU not start necessitating an air return.

Another required check is the crossfeed valve check prior to landing and being put in the logbook. That's something that tends to be easily missed as well.

I'm just hoping we don't reinvent the wheel too badly.