As of right now, it is just a one time offer for the nude version of this current public release. it will be tied to your account indefinitely, but it will not update alongside the main release. That said, we don't intend to release a nude version with every update here on itch.io.
This is mainly just a way to boost our budget on release with assets that we have already made. In the final version of the game, nudity will be incorporated into the story, and removing a characters clothing will have plot relevance, but that wont be for a while.