Bulletproof is difficult to achieve thanks to hardware failures. Additionally there is a wide range of older hardware out there that may not have been engineere

Bulletproof is difficult to achieve thanks to hardware failures. Additionally there is a wide range of older hardware out there that may not have been engineered with the necessary support (eg enough space to hold two copies of the firmware). But putting all that aside: the new sealed system partition is a step in that direction (ROSP was partially about getting clean separation between the system and user files to make snapshot-based updates possible). With snapshots if the update fails you still have the previous snapshot to fall back on - hopefully that will make these kinds of failures less likely in the future.