There may be options for the syntax, though.

Having dedicated syntax like define-library-alias has the advantage that each implementation can expand it to whatever forms that suits it.  But I'm wary about yet-another top-level special syntax.  And if it is allowed to expand into define-library form, where you can write it is limited, but it isn't obvious.

Another option is to extend define-library syntax, e.g. (define-library (alias <library-name>)).  This can also be interpreted as "import the named library and re-export all exported identifiers" (the name is debatable), and if so, you can add more definitions there to enhance the original library.  Pros are that (1) it is clear that it's define-library level meta-syntax and not an ordinary macro, and (2) in the latter form, you can put additional definitions.   Cons: it might be too flexible---too easy to write many libraries that adds little something to existing libraries, like what happened in the inheritance of OOP,