I'm a big mount collector myself, but yeah I have to agree that it probably won't stay unique. Very few skins in WoW stay unique.
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My shammy main is the one that uses the rarest stuff and then I usually stick to themes on my alts. Engineering/machine/plated (e.g. the ulduar drakes) on my goblin eng, dark or corrupted mounts or ones that look cool in shadow form on my priest, & on my worgen druid I don't use anything other than running wild as a ground mount.