I can't imagine DL would be sending out that sort of dramatic communication (man the battlestations!) for a increase in the AMEX waiver. FT's concern about the AMEX waiver has always been outsized. There's this mythical DL customer who spends tons of money on the DL cards but doesn't fly DL and is somehow less of a DL medallion than people who fly all the time.
Moving to one spend-based metric is the logical move and a more significant change. I don't love it, but DL has pretty clearly defined what they want out of their customers.