Relax OP_RETURN standardness restrictions

The discussion focuses on a significant bug associated with Wasabi, a notable detail outlined in a GitHub issue found at https://github.com/WalletWasabi/WalletWasabi/issues/10648, which became public in May 2023. The crux of the matter revolves around the challenges faced by the Wasabi coordinators in addressing this bug due to its discovery post the implementation of the mempoolfullrbf feature in July 2022, first integrated into Bitcoin Core with version v24.0.1 in December 2022. This feature's inclusion posed considerable difficulties for the Wasabi team, primarily because it took them several months to identify that enabling mempoolfullrbf=1 adversely affected their operations.

The narrative further elaborates on the hypothetical scenario had the mempoolfullrbf feature been released without an accompanying flag to toggle its functionality. Such a situation would have significantly compounded the challenges for the Wasabi coordinators by either necessitating a patch for Bitcoin Core or compelling the use of an alternative node implementation. This point underscores the importance of flexibility in software features to accommodate unforeseen issues.

Moreover, the correspondence sheds light on broader implications for users reliant on certain behaviors or options within the system, specifically mentioning datacarrier behavior/options slated for removal in future updates. It suggests a more lenient approach in the forthcoming release, allowing users the opportunity to adjust their infrastructure accordingly before these features are completely phased out. This recommendation aims to mitigate potential disruptions, providing a transitional period for users to either adopt different node implementations or adhere to version 29, thus avoiding abrupt adjustments.

In conclusion, the email from Boris Nagaev not only highlights a specific technical challenge linked to Wasabi and Bitcoin Core but also touches upon the broader theme of software development and management. It emphasizes the necessity of incorporating flexibility and foresight in feature releases, facilitating smoother transitions for users amidst evolving technological landscapes.