My 3 cents: To save issues with enterprise lawyers not approving to use your repo because it has a non standard MIT license, I would HIGHLY recommend creating a separate repo for the paid features, and leaving the open source one intact. A small additional effort to break your monorepo into 2, a huge time saver when you try to monetize it and realize this small addition goes from "automatically approved, regular MIT license" to "I need to open a ticket with legal as our open source compliance tools (e.g. blackduck) flagged it as non standard"