... is not a thing in software development.
Features are either deprecated, or not.
If they are planned for removal, they are deprecated now.
If they are not planned for removal, then mentioning deprecation in documentation makes no sense.
Topic on Manual talk:$wgLogos
In MediaWiki, "deprecation" is a formal process that involves documentation of how to migrate to the next step etc., which is not ready yet, so this is correct, if confusing.