Are house designs covered by copyright?

You could always write to him and ask him to specify a licence.

This is great. The more people subscribe to open source, the better it will get for everyone.

You joke, but developers can make profits with open source. The final part of the article deals with this issue.

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.