I'm sorry...I still don't really understand. This idea would not allow you to wield three weapons at once, so you could not have M79, XM, and Law, unless one of them were on the ground at you feet and you continually switched. But you could do that anyway. This idea would still constrain you to 2 weapon slots, it's just that you could decide to make them both secondaries when you spawn. I'm sorry that I'm not quite getting what you're saying.
As for the talk of law/law, I've softened a bit, considering that somebody wisely pointed out that law/law is essentially a weakened version of barret/law. (Out of curiosity, can you bink law?)