I think that's an excellent idea. If you think about it, it directly follows the same exact concept of "minimizing" and "maximizing" categories. You can minimize the ones you don't want to bother with seeing as you're not interested, and maximize them in case you want to have a look. Perhaps it could be integrated into a single feature? Or perhaps, integrated into a single feature, but also kept seperate. So that you could choose which forums to see the new posts feed from, but, it would automatically "uncheck" (let's pretend they're checkboxes) all the forums in a category you have minimized, as well as allowing you to re-check them regardless of it being minimized.
Not sure if you follow me, I'm tired. :D