I feel like a modern CS1.6 clone that is open-source, community run servers (only), no match-making, modable by design, could actually work. Even in 2025. Just needs some internet meme magic and a few dedicated devs
The problem with mods is that there will be a million different mods with a million different rules A million different levels and behaviors, and you won't get good traction on any any specific style of gameplay, and people will not keep coming back.