I like that idea, especially when you want to add many threads.
I'd probably just want to add one or two threads per resource ... so I'd prefer Just to be able to add a Tab or two.
The desire to add more threads to a resource is unlikely to be predicted by category. So per category permissions seem artificial. The way I saw it working was the Resource Authors themselves could decide how many threads they want. For example, if "larger/complicated" addons need more than one thread ... then ... can't every category of addon have a complicated addon ? It depends on the addon (resource) not the category.