In using the MIT License I see a few potential problems. 1st off you will be making your own competition. With Patreon being your major method of support you will be relying upon people to be willing to pay for exclusive features of having a say in how the game is developed while also enabling anyone to offer the same benefits.
On the subject of being able to make your game or portion of the game “cannon” I think that will end up being based on popularity. The most popular version/best marketed version would become cannon, while the official version and less popular versions would become ripoffs.
On that subject how do you plan on marketing this?
Here is my idea on how to improve your idea. First off focus less on making free to use games, and focus more on free to use software and assets. To explain further what you ought to do is design a game that is made of several parts. Those parts can be easily utilized independently, and your game is a demonstration of how they can be used together. You start out however without everything being freely available instead giving paterons a license to the items with the understanding that after a period of time those items would be re-released as a MIT licensed software or similar license. The completed game can be free to play as a marketing tool for the software, and you can eventually release it to the public domain You can also give patrons the ability to recommend features for the software and for the game prior to their release.