I'm tempted to close this as dupe of T56425, but since project is not the same, I'm not sure if there's a reason to have another task for this

Or even T76579

You seem to be right. It is not the same project, but @MarkAHershberger is the author of T56425: Provide an opt-in ability to register the user's MediaWiki installation.

Would it be better to merge this into T56425: Provide an opt-in ability to register the user's MediaWiki installation and reclass the project to wiki release team?

T76579 is the RfC discussion, and the result is accept/decline. Merged. Sorry, I was faster. :)

T56425 is the actual implementation if the RfC is accepted.

@Qgil, thanks for the clarification. I'll add T76579: RfC: Opt-in site registration during installation and T56425: Provide an opt-in ability to register the user's MediaWiki installation as blocking tasks when appropriate.