I would prefer to keep KePub out of the main calibre code, only because it's a single-site format that not even all users of the single site even like. It's also subject to change at Kobo's whims. Rather, I would prefer to ask Kovid to update (or accept a patch for)
https://github.com/kovidgoyal/calibr...ontent.py#L219 to allow a plugin to register itself as providing the necessary format support.