There should be separate aesthetic capes.

[Rilifane]

Capes! YES!
I would love to have capes. Some gear already hides tails and a drooping tail under a cape would only be natural. Tails have bone structure but if weight is added, animals just let it get weighed down by it because keeping the tail raised with added weight is too much effort and it would be the same for races with tails.
Some clipping will be unavoidable but we already have so much clipping ingame with hair and armor pieces, I honestly don't care. Besides, you can always chose to not use a cape with certain armor pieces if the clipping is too much.
The basic physics for it are there. Tacking it to the shoulders and the hem of a (theoretical) skirt lets it billow with movement and sideways with wind. Long skirts already billow sideways in windy areas. The effect wouldn't be strong enough to compare with real life physics but it wouldn't be some awkward board attached to your back. FFXIV doesn't have amazing physics but the basics for capes are there.

[Flay_wind]

Yeah, it has a cape - but unless it moves independently of the body (eg. can billow sideways in the wind) it would be what I was saying earlier: anchored to the shoulders and to the bottom hem of the hypothetical skirt that isn't actually there, but the movement programming for it is in place regardless.

I just checked. From the looks of it, the top half is indeed a immobile, and only the lower "skirt" part moves.
Well, that's how the things are it seems.