They have not indicated there will be any changes in MQD accrual on mileage seat upgrade purchases. Note the mileage price on these is always just simply the cash price at 1 CPM (minus the 7.5% US domestic excise tax charged on domestic flight cash upgrades -- you don't earn any MQD for the excise tax on cash purchases). Also, they have said Skymiles mileage awards on partner metal will now earn MQDs (unlike in 2023 and earlier) which seems pretty clear to indicate that MQD earn on DL metal awards will also continue.