What is the official bitcoin channel to request the OP_RETURN size change? (press often mentions that ethereum is good to manage changes and bitcoin a complete zero.

Here is the simplified version:

Most of these changes start with discussions like these, but then are moved concretely to a PR to bitcoin-core with the code changes (in this case there is no fork so pretty easy) and an introductory comment pointing to discussions elsewhere.

The conversation will also move to the PR itself. Part of the challenge now is getting review of your PRs - you’ll need to evangelize some and/or have social capital in the bitcoin community to get sufficient ACKs to your PR (and some NACKs which you will calmly addres), and someone will likely point something out you missed, so you revise the PR.

At some point hopefully there looks like all reasonable objections have been addressed.

If there is enough interest and few objections there will be discussions by the community & maintainers to merge it. It is this last part that isn’t very transparent, especially for even a good proposal. The maintainers, based on their sense of the community’s interest and consensus, must choose when to say it is ready, and then decide when and to which release they wish to merge it.

They often start by requesting you to revise your changes to be off by default, and be turned on as an option for a specific release. Often PR contributors know this is coming and include it.

Even once it is released, this type of change can only happen after sufficient miners and nodes update to the release and turn it on. If sufficient do, then the maintainers evaluate when to have the feature on by default.

These articles offers more perspective:

— Christopher Allen