BIP Draft: Flag day activation based on nLockTime signaling

This document introduces a novel process for activating soft forks within the Bitcoin network, proposing an alternative to the controversial BIP 8 and BIP 9 methods. It suggests utilizing nLockTime in transactions as a means for users to signal their support for specific soft fork proposals. This method entails assigning numerical values to different soft fork proposals, which users can then include in the nLockTime field of their transactions to indicate support. The inclusion of these transactions by miners in new blocks would serve as a signal of readiness for the proposed soft fork.

Furthermore, the document outlines a procedure where, after a three-month period of signaling via nLockTime, the community analyzes the transactions to gauge readiness and prepare for a "flag day" activation of the soft fork. This approach allows for a clear and straightforward demonstration of community and miner support for changes, bypassing the complexities and issues associated with previous activation methods.

Included in the proposal are links to reference implementations showcasing how the activation process and exclusion from relay or mining would function in practice. These references are vital for understanding the technical feasibility and implementation specifics of the suggested method. For instance, the activation process is demonstrated through a commit on GitHub (activation), while another commit illustrates how transactions not aligned with the new rules could be excluded from relay or mining (exclusion in relay or mining). Additionally, the document addresses the possibility of transaction replacement if a user's transaction does not get included in a block within a significant timeframe, suggesting that users can replace it with another transaction using the same inputs but a different nLockTime.

By providing a clear, structured path toward soft fork activation that relies on direct signaling and community consensus, this proposal aims to address and mitigate the controversies and challenges associated with earlier methods.