A good way to handle the who-updates-the-updater issue is to use a triple partition updater. A updates B, and then B updates C, then C updates A. If anything about the new version prevents it from properly updating its neighbor, that neighbor won't be able to close the loop, and you'll fall back to A. This simplifies the FSBL, because it just boots the three partitions in a loop, no failure detection required. You don't need to triplicate the full application either, just the minimum system needed to perform an update, and then have the "application" in it's own partition to be called by the updater.