Fwiw, Chris has detailed in many podcasts that Mojo will definitely be entirely open source in the future, and that the only reason it isn't now is that he learnt from his experience running Swift as an open source project that the open contribution and planning model is a bad fit, and basically counter productive, at this stage of a language's lifetime.

That is why they opted to open source in stages (ie, the stdlib is open source right now, and they expect to open source the compiler soon).