Recently Gota_agua (uvas_magicas) archived a number of extension pages in MediaWiki. I do not oppose it, but it seems anyone can do such thing and currently there are no guideline about this. Proposed:

An extension/skin may be archived when:

• the extension/skin is incompatible for any non-EOL extension for one year
• the extension/skin is incompatible for any non-EOL extension for six months and there are replacement
• the extension/skin is obsoleted by author/maintainer for six months
• when there are consensus to archive an extension (anyone can open a proposal and discuss on Phabricator)

In any cases the author/maintainer of an extension must be notified after a proposed archival and at least seven days before any non on-wiki actions (i.e. Phabricator/Translatewiki/Gerrit/Configuration/tests/integrations).

Open question:

• Whether to consider how the extension is used in active wiki (e.g. Wikiapiary statistics)
• Some extensions have very specific functionality and are used in a very limited number of wikis, and it is not easy to know whether they are maintained or compatible (e.g. T271379: Archive the WikiLexicalData extension)
• What about extensions hosted at GitHub? When Wikimedia moved to GitLab the process may be changed as you can host your own extension at your personal repositories