A low pauldron greatly restricts arm movement - which is why we've never attempted to make one that attaches to our Neck Armor. However, a Pauldron that attaches to either the inside peg of a LEGO minifig arm or clip to the arm itself is more likely. However the former will prevent the arm from snapping in fully, leaving the latter solution as to the best. Ramus experimented with such awhile back but we didn't end up making them. I have my doubts as to how secure a piece would snap onto the arm - I'm wondering if simply making a new arm mold with such details is a better solution?
Maybe it could be connected to a vambrace? like a full cover piece for arms (minifigures do not have elbow articulation, so this would not limit movement).