I would personally prefer that they NOT upgrade more than a few passengers at the 5 day window and instead held a significant portion of seats until 24 hours. That way those of us who frequently purchase tickets on short notice at higher fares have a more appropriate share of upgrades. I cringe thinking that my flight tonight which shows only 1 F available is full of PMs or GMs on LUT fares sitting up-front while I sit in back with an $800 ticket. Maybe they bought F - I am sure some did - but I bet 50% did not.
^+1...and I think DL would do it if they could find a way of not causing mass hysteria. The higher pay deserves the better reward.