A Gender Fluid Life has a personal and interesting role of gender transformation fantasies over at YouTube.
Erotic crossdreaming refers to sexual fantasies where a person is transformed into another gender or is playing the role of another gender.
There are cis people who have such fantasies, in the sense that they find the switch fascinating, but are nevertheless anchored in the gender they were assigned at birth.
Transgender people who have not transitioned may also have such fantasies. They are, like cis people, sexual beings, and transformation fantasies let them explore the possibility of being their real gender. Since they often find it hard to establish a satisfying sex life living and presenting as their assigned gender, the very idea of a gender transformation becomes eroticized. Why wouldn't it? Becoming your real gender makes a matching sex life possible.
(Some refer to this as "autogynephilia" or a fetish or a "paraphilia". The autogynephilia theory has been thoroughly debunked by science, and it its explanation does not reflect the real lives of trans people. Forget about it!)
A Gender Fluid Life has published a series of four videos discussing the role of transformation fantasies among gender variant people, which you can find here.