First, I would love it if the cruise lines would enforce the codes they've already made. As Marc said, if they did this, we wouldn't be talking about it so much. With cruising the booming business that it is, I don't think the lines have to be afraid of losing business.
Second, I would love it if they did away with formal nights. I've been on enough cruises with formal nights and one cruise where every night was formal, including first and last nights. The elimination of formal nights would simplify packing, especially for women. A combination of semi-formal and casual would be fine for me.