so what is she then?

[Saikou]

I want to believe... I mean, its a freakin' dragon themed expansion...

http://finalfantasy.wikia.com/wiki/Gria

[Baithin]

I want to believe... I mean, its a freakin' dragon themed expansion...

http://finalfantasy.wikia.com/wiki/Gria

It's dragon-themed, but Yugiri herself (and presumably other members of her race) is not from Ishgard, they're from basically the other side of the world. I don't think the new race will have anything to do with what's happening in Ishgard, other than Yugiri's possible involvement.

Regardless, I still think the "Auri" are reptilian, at the very least.

[Zetsumei_Tsunarashi]

People have speculated that the protrusions coming out of Yugiri's head could be either ears, or horns. From watching the main story cutscenes I think we can definitely rule out that they are ...

...horns. When we see yugiri in coerthas, at least when I was watching the cutscenes, the wind was blowing. And her ears were blowing with the wind. I think it's safe to assume that horns would not be blown around by the wind.

So by judging from the scales on her tail and the floppy ears, it's looking more and more like she's some sort of beast/reptile hybrid.

[Empressia]

What of the Garleans, then, are they part of the 5 races? Or are they another hyur "tribe"?

Overall, I don't think she's a beast tribe at all. Somebody mentioned an "Auri" this may atleast be the name. Who knows, maybe having a -ri at the end of thier names is part of thier naming convention

Physically they're just blondies highlanders, however if we count Allagan descendant and genetic manipulation, i'm goin to call Garleans are "mutant hyurs" just like Xande the "mutant Roe" in which the Garlean's third eye function isn't really revealed and the fact they can't use magic or aether manipulation in line with Xande's mutant ear shape and complextion.

[Black91CRX]

It's be FF's version of an Argonian (elder scrolls) I bet.

[Balipu]

So she is a dragon-rabit? Drabit? Makes me wonder if the name Mistwalker refers to her race or her ninja-ness? Whatever the case we can be sure that her very dramatic unmasking will reveal the new race. Imagine Yugiri fighting the bad guy of patch 2.5. A sword slash removes her mask and underneath we see a dragon face that megaflares the hell out of him.

[axemtitanium]

Mistwalker is a reference to Hironobu Sakaguchi's (creator of Final Fantasy) new company, Mistwalker, which has made stuff like Blue Dragon and The Last Story.

[Saikou]

I just want to believe, Zetsumei, I just want to believe. Her form looks more like a snowy rabbit with a long tail. I would like it to be a straight up Ivalice race, such as Vierra, but get the definite sense that its going to be something completely original.

[Dioptase]

Well look at the patch notes about ninja and you'll see thumpity thump thump

[Alenore]

Well look at the patch notes about ninja and you'll see thumpity thump thump

This is actually the most convincing argument I've seen so far.
(However they pretty much confirmed it was not bunnygirl in the live letter, so...)