Hey folks,
I suspect that the Torn Invitation stopped dropping from Nightfallen Caches around 9/13. Lots of people you see riding around on the fox got the Torn Invitation before that date, but nobody I know or strangers I have asked in-game has gotten it since then (i.e. I see someone on the mount, I ask them when they got the quest starter item, and so far everyone has given dates in early September.) Wowhead reports of getting the quest item stopped around mid-September as well.
It wouldn't be the first time Blizzard decided something they intended to be rare wasn't rare enough and nerfed it into oblivion - I'm just starting to think it's not dropping at all. At the very least, drop % seems to have been severely lowered.
Have you gotten the Torn Invitation from a Nightfallen Emissary Cache since 9/13, which was 5 weeks ago? (Please note: I'm not talking about receiving the actual mount, which requires a number of steps including time-gated class hall missions - I'm talking about the Torn Invitation which begins the quest chain.)