A lot of old games have become unplayable on modern hardware and operating systems. I wrote an article about how making games open source will keep them playable far into the future.
I also discuss how making games open source could be beneficial to developers and companies.
Feedback and constructive criticism are most welcome, and in keeping with the open source spirit, I will give you credit if I make any edits based on your feedback.
You’ve laid out one potential development cycle: FOSS from the get-go, and open collaboration welcome.
However, that’s not the only way that a FOSS game might be developed. The code could be freely licensed, but the upstream developers refuse to accept outside patches. In that case, there’s one “original” and then if you don’t like it, build your fork.
Alternatively, a game could be developed entirely in-house under proprietary licenses, and then only made FOSS upon commercial release. Contributor patches could improve the project, but conception of the game would be entirely the domain of its original developers.