I think the vast majority of DL pax use the A/S checkpoint, which doesn't have a priority lane.
I went through the A/S checkpoint two weeks ago. It most certainly DID have a priority queue (which I got into using my AS MVPG card, even though I was flying WN, though the backup was still fairly heavy- about 15 minutes WITH cutting in line using the priority queue) I believe DL PMs get privileges at the A/S gate checkpoints at SEA, though I would have to see the sign to be sure. AS elites get in at ALL the checkpoints, since there are AS/QX flights out of N, D, C and A.