Taking a second look at OP_EXPIRE

The concept of Miner Extractable Value (MEV) introduces a scenario where miners might choose not to process certain transactions, leading potentially to the expiration of these transactions and the loss of funds. This situation is considered somewhat hypothetical and would require a significant compromise of the Bitcoin (BTC) ecosystem to become viable. In competitive mining environments, where profits are slim and primarily derived from transaction fees, especially after the cessation of emission rewards, ignoring high-fee transactions could disadvantage a mining pool by driving hashrate elsewhere. The mobility of miners between pools mitigates the risk of any single pool gaining too much control or neglecting profitable transactions.

The debate over MEV becomes more complex when considering 'selfish mining', a strategy highlighted by recent attacks on Monero. However, comparing Bitcoin and Monero in this context requires caution due to their differences in hash rate, market capitalization, and mining infrastructure. Monero's lower hash rate and unique economic model, including perpetual tail emission, distinguish it from Bitcoin. Moreover, the lack of specialized hardware for Monero mining reduces the financial stakes for miners, contrasting with the substantial investments required for Bitcoin mining operations.

The dialogue extends into the philosophical realm, particularly regarding the proposal of an expiration opcode for transactions within the Bitcoin protocol. Despite potential vulnerabilities to MEV-like tactics, as demonstrated by the Lightning Network's reliance on timely transaction confirmation, an alternative approach to transaction expiration is suggested. Rather than introducing new opcodes, the same outcome could be achieved by confirming alternate versions of a given transaction, thereby rendering previous iterations invalid without necessitating changes to the consensus mechanism. This method also addresses potential issues in protocols involving private key transfers without replacing the specific functionalities proposed for OP_EXPIRE and OP_CSFS, except in cases where updating external state information necessitates the creation of new UTXOs to invalidate prior confirmations.