I also REALLY like it and have been wanting some kind of weapon sets or quick swapping for awhile now but never knew how to balance it. How does quick swapping not just mean the player essentially has EVERY weapon equipped as long as he's willing to to manage the swapping?
Tying it to SP is a great way to not only give this a decent restriction but it helps continue to expand SP into a proper 'game system' which seems to be a sort of running theme lately.
This is definitely going to have to be an EA thing since it will need quite a bit of interface stuff but I think you've solved a problem I've had for awhile here so big thanks!