Hm. So right now there are three unique ethereal mounts, the Polar Bear, the Boura, and the Charger of the Fallen. The other 11 were all made after the tameable version was released. The tiger would make it four unique ethereals.
The way they kept talking about "new mount," I really did think they were making a counter argument to the Cu Sidhe. If they made a tameable tiger after the fact, it would be the first time they have released a unique ethereal only to then make a tameable of it as well.
Strangely enough, I don't recall many people asking for tameable Polar Bears after the fact. I've seen people ask for Cows, Bulls, Great Harts, and of course horse armor. Hm. Well, the Charger of the Fallen was an event-specific ethereal, so it made sense to be unique (until they began selling it for cash). The Polar Bear was a fun veteran reward, something rather unique at the time. The tiger, likewise, is
rather unique. Looks like a bengal tiger. The distinction, of course, is there have been polar bears in the game since at least T2A. I feel like it's kind of a waste to not use the tiger art assets in the same jungles as jaguars and the like. Maybe they don't necessarily have to be tameable, but I say use them.