It's worth pointing out that @role was defined quite a long time ago, in its own specification, called XHTML Role Attribute Module [1]. It is this that provided the foundation for the ARIA work, which essentially defines a series of values for @role.
This may sound like nit-picking, but the whole premise of @role was to provide an extension-point for many different technologies, including those that we haven't yet thought of. ARIA is merely one such use of @role, and to co-opt it for this one scenario would weaken its usefulness.
[1] http://www.w3.org/TR/xhtml-role/