This project might not even get to novella length; it might end up in the neighborhood of very long short story. But this story has been waiting a long time to get told, so I don't think it minds how long or short it is. And there are no length requirements in self-publishing as there are in conventional publishing. Stories can be as short or long as they need to be. An awkward length no longer needs to be a reason for a story to not get written and published, and stories no longer need to be cut down or padded out to meet some arbitrary length guideline.
This is a good thing.