You should be able to pick up any item in the game if you have enough strength to pick it up. That being said, you should be absolutely terrible with them if you don't meet the difficulty requirement. So you can pick up shields, but if you're not up to the proficiency, it will raise very slowly, and break a lot easier than normal.
Same with a bow and arrow. Someone with 0 PD should be able to pick up any bow in the game (if they have enough strength) but the arrow will go completely off target when you go to shoot it.
I think this would be nice just for the fact that you no longer will be trying to pick up a weapon and a bow is covering it, and makes it impossible to pick up. You could also then run bows/shields back for teammates in strat battles.
I know I've suggested this same thing before, and I think others have as well. But don't get your hopes up.