Just as another way to visualize this suggestion (from an implementation standpoint, I guess), this could also work if the "subscribed forums" (categories) setting would subscribe you to all new threads in those categories. This would also allow an explicit unsubscribe to prevent future notifications. Even better would be if it was in a tree format where it showed the parent category.
I just subscribe to 4-5 categories and pretty much read those exclusively. But every time they have activity, I have to open the category, then open all of the threads. Not that big of a deal but I'd subscribe to a few more if all of the new threads were aggregated into one spot. I'm more interested in it from a perspective of threads than posts, personally, so this particular route is better. Not sure if this is the experience you're seeking. The new posts feature just seems to nurture "internet disease" to me.