Relax OP_RETURN standardness restrictions

In the exploration of block propagation within blockchain networks, particularly those mirroring Bitcoin's architecture, an intricate analysis reveals the nuanced dynamics between compact block reception, validation, and relay processes. The initial reception of a compact block by a node triggers a comprehensive validation process. This procedure is paramount to maintaining the integrity of the blockchain. However, should the compact block contain transactions absent from the node's mempool, it necessitates fetching these transactions from peers. This requirement introduces a potential bottleneck in block propagation speed, as this additional step could be replicated across each node, thereby amplifying the delay.

The discourse shifts towards a proposed optimization aimed at alleviating the identified propagation lag without compromising the network's security fundamentals. The suggestion entails a revision of the block relay policy to prioritize the checking of a block's adherence to the proof-of-work (POW) target before its relay across the network. Subsequent steps include the validation of the block's contents followed by its application. This approach aims to mitigate the 'per hop' delay attributed to sourcing missing transactions by decoupling the initial relay from the validation of block contents. While this strategy introduces the risk of nodes relaying invalid blocks—a scenario deemed economically unfavorable for the attacker—it underscores the potential trade-offs between efficiency and security.

Further contemplation on this matter highlights the implications for miners, especially regarding transaction inclusion policies. Miners lacking certain transactions are compelled to procure them to ensure the legitimacy of their subsequent blocks. The discussion subtly nudges towards strategic peer connections and adoption of permissive relay policies, exemplified by tools such as librerelay. This strategy is posited as a measure to diminish the likelihood of encountering missing transactions, thereby streamlining block propagation without significantly undermining the network's robustness.

This discourse, set against the backdrop of the Bitcoin Development Mailing List, encapsulates a critical examination of blockchain's block propagation mechanisms, proposing nuanced adjustments to existing protocols to enhance overall network performance while cautiously balancing the inherent security considerations.