Hey Sindri, thanks for getting the game. I'm glad you're enjoying it! :)
The Patreon companions are only 2 out of a total of 20 we have planned for the game. They'll remain exclusive to the higher Patreon tiers for the time being, but we may revisit the issue once the game is finished (possibly making them available as a one-time optional purchase like you suggested, though we'd probably bundle them into a DLC with some extra content and gear to add more value to the package).
P.S. SINDRIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII!!!! :D