One pain point associated with FCV right now is that there is no guarantee that an FCV transition happens in the same order with respect to other oplog entries on the primary and secondaries, which means that for a given oplog entry, if we were to check the FCV while applying the oplog entry on both the primary and the secondary, they may not have the same FCV. We should investigate if we can serialize this so that it happens in the same order on all nodes.