I like the idea, but it was already a stretch for us to add Nathan to game so we have no plans to add any further unplanned character routes.
But I do fully support modding the game so if you'd like to unpack the game (Using Unren) and make a mod adding in Kai yourself you're more than welcome to. If you have any questions in regards to how the game works and such you can reach out to us on our discord server.