Fine. Replace use/burn with expire/breakage elimination.

I still don't see why it makes any sense to restrict Skychoice... if you were stuck with a walk-up fare situation, and couldn't get last-seat Y availability by miles, is it a given that you'd give Delta your money? As an award ticket, you're more or less stuck, but as a cash ticket, you may well have choices, and not just with Skyteam.

The major mentality shift I can see would be to make people more likely to burn miles on Skychoice, by virtue of it no longer being an absolute fallback. Which I suppose is "good" for Delta, but it's terrible for customers.