787s are powered down if they are not going anywhere for a while and servicing or maintenance is not required. It happens regularly.
Powering up a 787 takes longer than most legacy aircraft but it's not hours. Neither is it painful.
As long as you do it right.
At BA, we normally didn’t power down between flights, however:
there was a problem discovered by Boeing, that if a 787 wasn’t powered down after a certain period of time (128 days?), there could be problems. So, the engineers had a schedule of “de-powering” each tail number on one of the occasions that it passed through LHR with sufficient turn-round time.
I had some status messages once at MEX which the engineers couldn’t clear, even though the originating fault had been fixed. After much head-scratching and liaison with London, the answer was to completely de-power the aircraft, leave it dark for 20 minutes, and then carefully power-up again.
Unfortunately, it was night, so all passengers had to be offloaded. Not normally a problem but we had 35 wheelchair users on board, so it took a while….
But it worked!