I was going to hold back on this thread, but it's getting a little ... weird. Let's talk big pictures.
What are they?
A quick look back to the options given in the early Players' Polls suggests that Au Ra were internally built on the concept Reptilian Demi-beastmen. This is similar to how the Miqo'te are Mammalian (Feline) Demi-beastmen, or how a Viera-like race would have been Mammalian (Leporine) Demi-beastmen.
So, the dev. team goes through a few stages, bringing in demon-like concepts, and dragon-like concepts, and, what the hells, some of the wolf-like concepts from the mammalian considerations. Taking the aspects that are (seen internally as) best from each, the Au Ra takes shape, and it's quite scaly. What's the first thing that pops into your head? Most likely? Scalekin! Drakes and and the like! And the dragons descended from the Celestials! So they started fleshing out these early Reptilian (Draconic) Demi-beastmen.
However, as development on the story came along, they ran into a small problem. Isn't this the Ishgard expansion? Isn't Ishgard embroiled in a dragon war and don't they hate everything even vaguely related to dragons? And - oh, great - now people are running with Ishgard's accusation that Hraesvelgr and Shiva's spiritual bond can be reduced to a carnal and heretical sin, and that these "Au Ra" are their offspring.
"How can we fit this race into the story without alienating them right off the bat?" Time to walk back the emphasis on Draconic and highlight the Demonic undertones a bit more, for starters. But let's keep enough of it to highlight the tension they would have in Ishgard. Let's leave this debate to "the scholars", but overall weight the scales (pun intended) on "not dragon" pretty hard.
Or did Hypothetical Othardian Celestials have something to do with this? Speculate, speculate, speculate! <foot still on the scale, though>
"They're too Hyuran"
Ironically, the reason we didn't get bunny people is that they were too Hyuran. Take away ears and tails and the Viera and Miqo'te are essentially Hyur. Yoshida especially thought the males were not beastly enough - too cute. This seems to have been heavily exacerbated by the fact that "how can we cram as many gearsets as possible into this game" has clearly skyrocketed into the dunklesphere on SE's list of priorities, so races got simplified into very slightly modified Hyur wherever possible (this is why you're probably never getting your Miqo'te butts back). Thus did SE go with an option that they could make slightly less Hyuran and slightly more beastly, but without extending their gear development time by 33%+.
Maybe one day we'll get a definitely-not-all-that-Hyuran race...
But I'd assume you'd have an easier time convincing them to make bunny boys, at this point.