Unbreaking testnet4

In a recent discussion on the Bitcoin Development Mailing List, several key points were brought up regarding the evolution and management of Bitcoin testnets, particularly focusing on the distinctions and implications of certain changes compared to the mainnet. The conversation shed light on the rationale behind not incorporating specific types of changes into the Bitcoin mainnet due to their deviation from its intended design and function. Among these changes were the signing of all blocks in Signet, the concept of an unlimited supply, and the lack of reset logic in the new Testnet5's consensus rules. These elements are considered significant deviations from the original chain's philosophy and operation, prompting a cautionary stance against their inclusion in the mainnet.

The dialogue further explored the potential longevity of testnets when they lack a reset mechanism, highlighting concerns that without such functionality, testnets could theoretically operate indefinitely. This scenario has led to observations that Testnet3 is evolving into an alternative cryptocurrency (altcoin), a development trajectory that future testnets might also follow if substantial modifications aren't made. The discussion pointed out that while Signet has not been traded due to its centralized mining approach, the existence of centralized altcoin federations suggests that this status could change, leading to broader implications for its usage and perception.

A crucial aspect of the conversation centered around the concept of "reset" versus "abandonment" for managing testnets. The idea was proposed that instead of resetting, which would imply reorganizing an old testnet's chain by creating a stronger, alternative chain in Testnet5, it might be more appropriate to consider abandoning the old network. This approach would involve building upon the same Genesis Block to produce a backward-compatible, yet more extensive chainwork, thereby replacing the old network in a manner that respects the continuity and integrity of the testnet's history and purpose. This nuanced perspective underscores the complexities involved in maintaining the relevance and functionality of Bitcoin testnets while balancing innovation with adherence to foundational principles.