Blizzard has added a yellow crystal snail mount to the game in the latest 10.1 PTR build. However, it currently has no source and we don’t know how to get it.
Embers of Neltharion adds multiple new crystal snail mounts, but only oneĀ (Big Slick in the City) has a source thus far. The latest build includes a yellow variation of the crystal snail mount. With their Deepholm vibe, I’m sure they will come from Zaralek Cavern.