Malte
The best benefit would be to improve acs-subsite where you felt it needed to be improved, but a general solution to combining packages makes more sense to me than to custom code every time a new package comes out and you want to relate it to project manager.
I don't see .LRN communities as anything except a special case of acs-subsite. There has been a great amount of work done to make subsite creation with packages setup and .LRN should move to use these facilities. That way a site could take advantage of the same type of community features with or without .LRN.
