Hi Stodge,
The short answer is no -- there are no plans to do what you describe.
That said, what you describe shouldn't be too hard to write yourself. Permission checks are quite well abstracted into the auth backend, so you could fairly easily write your own authorisation app that adds a model that allows associations between Site and Permission (or site, user and permission - whatever you need), and an authentication backend that adds extends the base ModelBackend to also check your Site permissions.
Yours,
Are there any plans to change the Permissions to use the sites framework? To support multi-site on my site, I need the ability to assign different permissions to the same user on different sites. Alternatively, any suggestions how to achieve this? Thanks