I think the idea of chastity is mainstream but in a different context than the fetish style we know of it as. for example a lot of historical religious text have implied usage of chastity for pre-marital girls. i cant think any of specific examples for actually using devices but i think chastity belts on girls has been a long maintream thing because of religion

the male devices on the otherhand werent really popular even within the fetish community until the cb series and a lot of people really didnt like the look of the cb series because they look really medical. i think cages like the holy trainer, which look more attractive and streamlined, are getting a lot of attention for the fetish.