I have mentioned examples of games that saw commercial success while being open source. And of course, delayed open source is also an option as some other users have said here.

I think it could be viable for a company to release a game with a “5 year FOSS promise” or something similar

Yes, that is one of the options I mention in the article. But there are games that are open source from day one, such as Mindustry, which have seen commercial success.

I agree, it is better to be open source all the way. I believe Godot became more popular after Unity tried to charge developers per install.

If you think all products should be open source, you might like this other article I wrote about making aircraft open source.