The 787 Dreamliner has been grounded

[Hobbes]

That makes zero sense, since ETOPS deals with the ability of the aircraft to reach a distant airport on one engine inoperative. .

It's been a while for me dealing with ETOPS but I'm sure you know better that Inspector. As you say it deals with the ability to reach a distant airport. That means ETOPS deals with anything that influences that, and a key area is fire suppressant systems. The hold, and this case battery fire suppressant and containment systems must be able to demonstrate the ability contain/suppress a fire for the same amount of time that the aircraft has to remain aloft for. I suspect if the FAA is pegging this back to 2 hrs then they don't have faith/ Boeing can't demonstrate the system is capable if this.

[The Inspector]

Following the inflight fire and crash of Critter 592 the aftermath made onboard lower cargo fire suppression systems mandatory, and if the battery containment vessel is vented overboard, I can't see an issue. The APU can be started and wil run without the battery charger being involved with the simple lockout breaker involved being deselected (HUH?... all but 50 or so, and no 'big' power comes above the cabin floor by use of RCCB's of 1/2 A each controlling bigger breakers @ the power panels, (thank you DC-10) circuit breakers on the 787 are virtual and require no manual manipulations) on the instrument control screens in front of the flight crew.
I'm still of the opinion that this is a CYA power play on the part of the clown college in Oak City.