Types don't take parameters, and I don't believe this is a valid use case that would justify introducing an extra dimension to the fundamental principle of the type system.

The other features should suffice in describing templates like like {{Tl}}.

We have wiki-file-name and wiki-user-name, for example. Because while those have associated wiki pages, they are their own object type. For example, files may not have a description page, or come from a foreign wiki. Users may not have a user page.

We could provide a similar types for other object types in MediaWiki. Depending on whether there's sufficient need for this. Candidates that come to mind are:

• Categories. (May not have a description page. Has existing API.)
• Interface messages (May not exist locally, plus the MediaWiki namespace includes subpages that are themselves not message keys. Has existing API.)

A generic "namespaced" page name type would be too generic and would encourage template constructs that are not user friendly

Templates currently do not have their own object type within the MediaWIki eco system. They exist as regular pages that can be transcluded as any other (see also T98562, which exposes this problem).

Still, we can create a "wiki-template-name" type and tie it to a namespace (even though it doesn't have its own entity type internally, like users, files and categories do). We need to be careful to not imply that this type accepts any valid transcludable page name, since virtually any kind could be transcludable.