Several in-game days later I went back to Arcadia's Cauldron to raid her barrels and displayed items, only to find they hadn't respawned. Went to the Bannered Mare, no respawned barrels. Went to the Giant camps I'd cleared, chests hadn't respawned. Waited 2 in-game days and checked again. Things STILL hadn't respawned.
Thinking maybe there was a level you had to be at before things started respawning, I loaded a save for my level 61 Khajiit and went through the process again. Raided Arcadia's store, several Giant camps, and killed a few Dragons. Waited several in-game days only to find stuff still wasn't respawning.
Now maybe I'm remembering things wrong. I know merchant chests will respawn every 48 in-game hours, but how often do barrels, chests, and displayed merchant items respawn? At the very least I'd assume displayed merchant items would respawn every 48 in-game hours as well, since those are (again I'm assuming) tied to the merchant chest. I'm fairly certain stuff has respawned every few days in the past; this issue w/ things not respawning only became apparent a few days ago.
Any insight as to what's going on would be appreciated. Truth be told I was sorta irritated at first, but it doesn't bother me so much now. It's more a matter of wanting to know what's going on rather than being mad it's happening.