For my two cents worth, turning that piece into a sleeve could work but would need some very deep thinking not to ruin how special it is now. Perhaps just a subtle shaded background (clouds, fog, water, whatever) to fill in the ‘white’space but not much else. And you’d also need a good border around the current piece where nothing except the same background was, again to keep it seperate yet whole.
Maybe if you turned the entire thing into some sort of insignia/shield design, you could get very sharp outer lines to break it from the rest of whatever would go on the arm, but I’m not sure how that would go…
