Saints Row 4 DLC
Solution 1:
Having recalled that I effectively jumped straight into the DLCs, with no partners unlocked or real progress made, I looked this up on the Steam forums.
Posting on a Steam Forums post entitled "How to access How The Saints Saved Christmas", [V]IdolNinja writes: How the Saints Save Christmas dlc unlocks after you get Telekinesis. You should get an unlock screen after completing the first Genki Mind Over Murder.
This makes the most sense, in review of my achievement log.