Personally I'm really not sure if a namespace is the best possible
solution. mediawiki.org is more a continuum of content we collected
over the years. Pages are rarely up to date. It would probably be less
cumbersome to consider the existing main namespace an "archive" and
only mark pages that are known to be up to date.
I'm also on the skeptical side. I think whether something is relevant is rarely clear-cut. I think most pages where the information is in some sense old, and cannot be fixed just by updating the page, fall into one of these categories:
- The page documents a thing. The thing still exists, but isn't important anymore. Maybe it's not used by Wikimedia, but used by others.
- The page documents a project. The project is finished. The page is not outdated (since the project finished, there is no need to change its description) but not that relevant to present-day capabilities.
In both of these situations, it's not that obvious whether the reader would want the page included in the search results or not.