Per FCOM, "The APU starts and operates up to the airplane maximum certified altitude", so there is no problem starting the APU in flight--no need to leave APU running from pushback.A major US-based NG operator's FCOM says to run APU when flying ETOPS segment. Also, to operate the fuel crossfeed valve in the last hour of ETOPS to ensure that crossfeed works for the next ETOPS flight.

For the SEA-OGG flight, the logic is this: the cost of two APU cycles is more than the extra fuel burn before the ETOPS Entry Point (EEP). Remember you have to have the APU on before EEP.Another operator I worked for had you leave the APU on if you were to enter ETOPS less that 90 minutes after takeoff, otherwise start it 1 hour before EEP. That way you get a few cracks at starting the APU before you have to turn around.

Thanks for the responses everyone@599AS - definitely tell me when that happens, sounds interesting!

It should be approved in the next few weeks per the most recent bulletin. Its estimated to save over 2 million a year in fuel.