Since you can fly the 787 without an APU battery or APU, we're honestly saying that because one Ship's Battery failed in flight we should therefore determine the 787 is no longer suitable for ETOPS-180?
I don't think the batterymalfunction is the root cause the FAA is reconsidering; it merely wakens them up that they have certified a brand new aircraft to ETOPS right from the start, without it proving itself in line flying. First fix the teething problems (or prove that there aren't any), then let it become ETOPS