If they limited upgrades to K+, I'm finding another airline to fly. They already have the upgrade system favor flyers in higher classes by ordering the upgrade list in order of class after status (which is fair). I could see DL going with a combination of fare+status and having a score for the combination so a GM buying a B fare has priority over a PM on a V fare. But, to limit it to K+ would reward poor planning instead of those who can book a fair amount of time in advance.

I would think that a better first class experience would mean more edible food and better drinks for those who partake.