I've actually spent the past 3 years making Easel (https://easel.games) specifically for gameplay logic. It's got behaviors as a first-class language construct, ownership and context is implied hierarchically, it's concurrent and event-driven to match how game worlds work, and the multiplayer is automatic because it's built into the fabric of the programming language.

It also feels like a declarative language because of the high-level constructs, but it is actually imperative because (in general) things get executed in the step-by-step order you specify, which I think is important because games are full of sequences.

It's been a lot of work but also a lot of fun! My aim is for this to be a great next step after Scratch for people learning to code but also a good model for how a more advanced game-making programming language could work in the future!

This looks promising. How come I hadn't heard of it??

My own ideas for an ideal syntax included keywords like "on" instead of "func" etc. (i.e. be totally event/signal driven)

Taking a look!