The pony and hair tie area where the hair loosens out is incredibly sexy. I absolutely agree with you that there should a genre of erotica for this. Very rare that we see in videos. I remember a Tru Kait video threesome where it happens and the hair tie ultimately falls out and its so damn good.

Please post if u remember more videos or see them

Here is the Tru Kait video:

(Its not the full version, but this the video)