I just noticed that i had a few BU nodes connected to my full node, what do you think would happen if all Bitcoin Core nodes blocked BU nodes ?
BU or Core doesn't matter only Core rules are obeyed. it's an open source community and they'll run 1 Core node to sync with their BU nodes.There are some technicalities which I might point out after thinking about them.
Only thing matters is the miners with actual computational power and the majority of miners are currently using Core software(validating blocks and including them in blockchain that Core nodes relayed to them.