Huh, I had an idea recently to make an API-only game like that. Would let people build their own tools/GUIs and go as crazy as they'd like with building their own AI to control their empire. Just feels extremely niche, even if it scratches my own gameplay itch.
I'm concerned that such a game would be so much more rewarding to me as a developer than my actual software development job is, that I would become miserable at work!