I wish all the cruiselines would follow NCL's example and make formal night optional. There's no reason why those who wish to dress formally and those who don't can't co-exist on the same ship without one group being relegated to a buffet or other inferior dining alternative.
I think it is heading that way anyway, at least unofficially, as more and more people decide to forego the formalwear in favor of more casual attire. On my last Celebrity cruise, on formal night there were many people dressed to the nines, but there were also many others wearing dressy-casual (including myself). Both co-existed peacefully and I didn't see anyone being turned away at the door.