I think taking a highly abstract definition of backcompat is not useful. We need a practical definition of back compat. If there are no (or effectively no) down

I think taking a highly abstract definition of backcompat is not useful. We need a practical definition of back compat. If there are no (or effectively no) downstream consequences of a change, it is clearly backcompat. If there are some downstream consequences, you get into judgment call territory, but it still may be worth it. We cannot create a perfect universal rule here, and Amos is a fool for holding that standard so rigidly.