However, not knowing if 2x has wipeout protection, detection may get a whole lot harder than just hardcoding a header hash and checking against it
... This piece of the puzzle is easy and already well-understood. I had assumed that btc1 was going to insist on it's forking-block being over 4MB in weight, a simple and elegant solution to the wipeout risk.... They couldn't possibly be stupid enough to not do that, could they?
Both methods fail anyways, since they do not provide a strong guarantee of replay protection to begin with
I don't understand? If I have a pre-split UTXO, and I send it back to myself with their magic value in an OP_RETURN the transaction is not valid on the btc1 chain, and the resulting UTXO may be spent freely with no risk of replay, and can also be used to taint other UTXOs [At the expense of privacy]. Once the BTC transaction is confirmed, the same UTXO may be spent freely on btc1 with no risk as the UTXO is already spent on Bitcoin....