(Sorry for the short update, I’m traveling):
For flights booked after December 15th, Delta many Silver Medallion members will only be able to check 1 free bag (instead of the current two) (details here).
Silver Medallion members with a Reserve, Platinum or Gold Delta SkyMiles Amex will still be able to check a second bag for free. Small consolation, I know. This is especially annoying, because most other US airlines permit 2 free checked bags at the lowest Elite level.