So, MMO-champ posted their video for the new horse mounts coming in Legion:
https://www.youtube.com/watch?v=17quANa3xDs
You can slow it down and take a look at the animations, or you can just look at the one that the current Warforged Nightmare uses in-game. They're the same.
These animations are pretty bad. Honestly. You don't even have to know what a horse actually runs like to tell that there's something very strange about how they run. It's very bouncy, and awkward.
Well, let's break down why it's so bad. Here's some stills of a real horse running:
http://i.imgur.com/6F1julY.jpg
First thing I'll point out is look at the horse's back. It is almost perfectly level the entire time. There isn't a lot of up and down movement in the horse's main section at all. Second thing, look at how far apart its feet go. A horse in full run takes really long strides. Some of the strides even take up the whole frame end to end.
And here's some stills of the animation cycle for the Warforged Nightmare:
http://i.imgur.com/1ZhirRy.jpg
It's actually very easy to see the comparison to my first point earlier due to the big golden circles on the Nightmare's joints. On a real horse, these would stay level through the whole cycle. They're all over the place. The back end raises significantly.
And on my second point, the Nightmare doesn't ever extend fully like a real horse. There should be at least one frame where back and front feet are at their furthest out at the same time, but the closest we get here is frame 6, and the back feet are bent really awkwardly.
This, unfortunately, isn't much of a new problem though. Blizzard seems to not be able to figure out horses, even though they had them right in Vanilla.
Five years ago (yes, five years ago) I made a video and a post complaining about the animation changes that happened in 3.0.
https://www.youtube.com/watch?v=KvJvZp4Lygg
And the post references the video I made two years before that:
http://us.battle.net/wow/en/forum/topic/2325034399
This was the result of their being two different animations pre-3.0, one for horses with "skirts" (epic undead mounts, paladin horses) and one for all the other non-skirted horses (human horses, DK horses). The two animations can be seen in my crappy video above. As of now, there are no more horses on the original pre-3.0 non-skirted animation. We are left with the bouncy, jarring animation on every horse. I still will never understand why a perfectly good animation was removed completely unnecessarily. It already existed, why change it?
Honestly, I had given up on the regular horse mounts ever being fixed. It's long in the past now, and I doubt anyone at Blizzard cares enough to justify or explain why a clear downgrade was made. I'm more concerned that we are getting new horse mounts that are an even further step in the wrong direction as far as animations go. Why can such a huge, successful company not figure out something as simple as animating a horse? They're not some huge complicated creature. It's a horse. A simple ol' horse.
I will say that thankfully the horses using Invincible's skeleton are done decently well to the point of not being obnoxious, so at least I'll always be safe on my favorite pony. Hopefully.