Functional Programming hasn't even been tried for game development, really. There is a lack of overlap between the game dev industry and academia. The studios are (rightly) risk averse and try to use the same broad strategies to build games - OOP, maybe ECS for large swarms, etc.

Personally, I think that FP could be a great fit, but we first need to come up with architectures that solve real game development problems. We have to do this with small scale experiments first (game jams are perfect for this) and then scale up only if they succeed.

This project is exactly that - kudos to the author.