I think it would be sad if the cruiselines would relax the dress code for the dining rooms to suit the few rebels wqho are determined to dress "their way". Since the dress expectations are clearly stated in materials we receive from the cruiseline with our travel documents, and are also stated in the website information, it's not as though people don't know what is expected.
Being on a cruise is an escape from the ordinary. Jeans, shorts, scruffy t-shirts are the "ordinary". So why not leave them at home, and play the part of a cruiser. Dress for the occasion and the location. It's very special, and happily, the majority of passengers see that and dress accordingly.