Does BU even have replay protection ATM? From what I understand, they may fork it if they have over 80% of the hash, but what happens if the tide turns, and the CORE 1MB suddenly has more than 50% of the hash? When the small block chain eventually takes over the BU fork, are the BU nodes going to switch to that chain and basically erase the forked chain from memory? That would be a disaster for anyone running the BU chain.
While your nightmare scenario is technically possible, so are hash collisions.
Nonetheless, any node is free to use the existing invalidate block mechanism to ensure it will never follow the temporary loser eventual overtaker.
Bitcoin Nodes don't relay a more than 1Mb Block size, it's all.
Simple.
The majority win.
Miners are not the majority, they follow the path (of all nodes).
The large block miners will not require small block nodes to propagate their solved blocks. Small block nodes will be routed around. Node operators can choose to follow the operational chain that is processing the bulk of transactions, or they can choose to follow the essentially non-operational chain which is nearly stalled. Nodes have that right, and they have that ability. Other than that, non-mining nodes are powerless.
You talk calmly like you know what you are talking about and you know what will happen. You don't and you can't.
Are you asserting that nodes have the ability to cause one miner's solved blocks from reaching other miners?