A new story featuring transformation of woman into an Equestrian pony, has been released by Chatoyance, known mostly for stories in which humans turn into ponies. This time, however, the setting is brand new: the story takes place in present day New York, not in dystopian future and there is no Equestria in existence in this story.
I.D. - That Indestructible Something

A young woman awakens transformed into an Equestrian pony - yet no other human being can perceive her new body in any way whatsoever. With clumsy hooves, but a bright mind, Gregoria Samson must trust in herself to discover the incredible, monumental truth behind her impossible change.

The story gets updated again!