Looking at fine print, spend on any DL-branded card should count:
Eligible Cards are the following: Delta SkyMiles® Platinum Card, Delta SkyMiles® Reserve Card, Delta SkyMiles® Platinum Business Card, and Delta SkyMiles® Reserve Business Card. Other Cards are not eligible for the MQD Waiver. However, if linked to the same SkyMiles number, eligible purchases made on a Delta SkyMiles® Blue Card, Delta SkyMiles® Gold Card, Delta SkyMiles Business Card, or Delta SkyMiles® Gold Business Card will continue to count towards the MQD Waiver spend threshold requirements.
So theoretically, if I expect to exceed $25k Amex spend by EoY, I could upgrade/open a DL Platinum card before year end to receive the MQD waiver. I wouldn't expect to qualify for the bonus MQMs though.