Its a softfork that you wouldn't even have to upgrade to. Right now there are at least 4 merge mined sidechains. Only the miners running the sidechain software can merge mine. BMM removes the need to run sidechain full node for L1 miners to collect sidechain txn fees. It literally alleviates miner centralization with things like proprietary sidechains using out of band checkpoints that could siphon off txn fees in the long term.