First off, this would probably be better in the Suggestions forum. The class forums are more for players to discuss issues related specifically to the class, the Devs don't usually look here for ideas. Secondly, they don't all work the same. Attacks from the Demons set inflict a -res effect. Attacks from the Necromancy set inflict a -acc effect. Even if the technology existed for allowing power swapping between sets, which it doesn't, they wouldn't because it wouldn't be an equivalent trade.
Edit: If you want a bow and arrow power, though, there's a temporary power you can get an infinite number of times via Ouroboros. http://paragonwiki.com/wiki/Bow_and_Arrow.
Since all MM work the same way as far as what each MM power is (attack or pet), I'd like to be able to switch the attacks within the powerset. For instance, I'd like to switch out the Call <animal> attacks for Bow attacks.