Additional notes (March, 2022):

A name that refers to a using-declarator whose terminal name is dependent is interpreted as a typedef-name if the using-declarator uses the keyword typename.

9.9 [namespace.udecl] paragraph 20 says,

If a using-declaration uses the keyword typename and specifies a dependent name (13.8.3 [temp.dep]), the name introduced by the using-declaration is treated as a typedef-name (9.2.4 [dcl.typedef]).

This wording does not address use of typename in a using-declaration with a non-dependent name; the primary specification of the typename keyword in 13.8 [temp.res] does not appear to describe this case, either.