I think Delta may find it very hard to turn around the mess their award availability has created. Losing flyers with top-tier status because of award price, availability and access is, in the old phrase, penny-wise and pound foolish.

Back when Continental starting limiting advance booking of international upgrades to status members, I took my business elsewhere. That was in the mid 1990s and I haven't been back (though recent improvements over there have me testing the water). Once they go, they're gone.