You do need to innovate on the foundation if you plan to maintain your game long term: new consoles support, new hardware support, obsolescence of old platforms, etc...
You do not need to innovate if you plan to let your game rot and become unplayable 10-20 years later.
Yes having a FOSS solution for the foundation would be ideal. That was not the topic of the discussion. The topic was about the claim "we can fork if we're not in agreement".
No, as a game developer you won't be forking and maintaining a game engine. No a "just fork it" is not a viable solution in the majority of cases as you need a strong community behind you and your fork to make it last long term and not rot after 2 weeks.