AA and UA continued tracking BIS flown miles for lifetime status. DL could continue the current MQM earning chart solely for lifetime status, could switch to BIS miles, or could base it on the new system.

Incidentally, I do think DL will switch to a loyalty points system similar to what AA and B6 have (and UA will tune their PQP program to similarly value card spending), because under the current system people who don't spend $25k/year on credit cards to earn the MQD waiver are not particularly incentivized to spend money on them besides earning SkyMiles. For personal spending, $25k/year is a lot to put on a credit card unless you put rent / mortgage payments on it, and not everyone can/wants to put business expenses on their personal card and be reimbursed. A continuous points earning system instead of a cut-off means DL can capture some of the $10k/year spenders who might otherwise use a 2% cash back card – the fact elite status is hard to put a dollar value on (and most people over-value it) helps make up for the lower value of SkyMiles.