Yes, I see where you ar going. The module has been for a same admin to manage more than one shop (as it is what we do). If you want an admin to only manage one shop, it means that you won't have common categories in between shop anymore ? The admin configuration is set as "default for all site" when you override the configuration of one site in a config file; if you want to make it for more than one admin, this would have to change too. I never really take time to considerate this improvement, and I think we should get more opinions about the needs of users before starting to do anything like that.

Also, I mainly started to make this module because it was something that my company needed, however, we don't need to have a specific admin for each shop, this is why I didn't bother doing it...

Customer table is common for all sites, it might have to change and be specific to one site (adding a collomn site_name to the customer's table...)

Well, this won't be ready tomorrow...