There are a number of "experimental" API endpoints in MediaWiki core.
The last substantial change to these endpoints was in December, 2020. (Subsequent git commits since that time were refactoring for compliance with unrelated core improvements). That's unreasonably long for an API endpoint to be "experimental".
I gave this "medium" priority (and considered giving it "high") because we will soon need to create additional "experimental" endpoints and the current situation both sets a bad precedent, and could complicate the new development.
Review the current "experimental" endpoints to see if they have value. If they do, promote to regular endpoints. If they don't, remove them. If any endpoints to be promoted have existing callers, provide a migration/deprecation path measured in weeks or months, rather than years.