What? Docker is still completely open source apart from the desktop GUI. The engine and (I'm pretty sure) all components are completely free and if anything, they have pushed for the standardization of the container runtime. Buildkit is free, compose is free, no feature is paywalled apart from Mirantis-centric stuff (not part of docker inc)
You can absolutely bet that they would get dropped like a rock if they moved to changing the engine's license. Even the docker desktop code wasn't ever open to begin with anyways.