Hmm, an intriguing idea for sure.
Regarding the rewards and all that jazz with the patreon, I'll present 2 ideas that I've seen out there:
- Have the game be 1 version ahead like you mentioned ( ala CoC2, TiTs, etc): This feels like a proper "reward" system for patrons, as it feels like you are subscribed to a still improving product instead of a unfinished project, but could potentially be unfair to the public audience if the amount of content added to one differs immensely from the other.
Or...
-Have it not be a version ahead and just use it for donation purposes: This one can be the most fair to both parties, as both patrons and non-patrons receive the same end product... but could potentially alienate (probably a strong word here, but you get the idea) some patrons in the future.
Either way, regardless of the pros and cons, you can do neither, either or both (have it be only for donations at first and then slowly accumulate content for an entire build, then release that same build for patrons at a later date) of them.
My Conclusion: To me, it doesn't really matter which way you'll do the monetization (be it Patreon or selling the game), as long as you keep making this lovely story better and better I'm not complaining.