I don't think that analogy works well, because if there was a dependency in standards that led to this outcome, would it not be better to break the dependency g

I don't think that analogy works well, because if there was a dependency in standards that led to this outcome, would it not be better to break the dependency going forward, or to have avoided it in the first place? And not having an ISO C standard for sign-magnitude machines (which is not a necessary consequence of the proposed change, it is just the worst case, depending on how ISO chose to deal with the consequences for such machines) does not necessarily force an end to actual C support for them.