Heart of the Aspects wasn't a hint, they used the skeleton of the MoP dragons because presumably they'd just started making them at the time. The skeleton was then skinned to look like the glowy thing the Dragon Soul shot at Deathwing.
So unless you're saying the Fey Dragon uses a model that is recognisably something else which points to a specific expansion, then no it's not the same thing at all.
In short, it's a cool looking mount and maybe Blizzard has a purpose for it and maybe not, but no it isn't a hint of the next expansion. Blizzard doesn't drop hints, they would tell you if they wanted you to know.
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2) Generic story hook left around in case they ever want to revisit it - which they keep saying they don't.