Death Knights should be able to have a class mount based on their race similar to how paladins each have a unique charger mount.
While this would be nice, I think it would be a large undertaking that’s not quite comparable to Paladins in scale. There are only eight races that can be Paladins at present, and even now with recent BfA additions Paladins still have shared mounts models between Human-Blood Elves (recolored), Dwarfs-Dark Iron (recolored), and Draenei-Lightforged (exact). The only truly unique Paladin mounts are those of the Tauren, and the Zandalari. (Someone correct me if I haven’t stayed updated on these.)
Looking to Death Knights we have twelve current races, and are about to add nine more. I’m not saying it can’t be done, just that it’s a lot more work that I feel your post is suggesting in its comparison, and I don’t think that a similar percentage could be shared models like Paladins have either.
Reskins might be more likely, in the same vein as some of the more undead looking skin tones we get for various races as Death Knights. With a few extra assets added to the textures for scars, peeling flesh, etc.
More mounts are generally considered good, but one of the best parts, in my personal opinion, is the unity of DK’s, regardless of race, in death. Same general aesthetics, class special mounts, and specialty armors. I feel like the race specific DK mounts would dilute our unity a bit much for my liking. Undead dragons and horses are plenty fine. We even have a gryphon, which could be seen as an alliance nod but i rarely see it used.
I’d rather aesthetic perks be pushed elsewhere if given an option of visual/cosmetic only updates.
With enough effort through archaeology you can get a bone raptor, which works for the only important DK race, trolls.