+5 insightful. Programming language design is all about having the right nexus of features. Having all the features or the wrong mix of features is actually an anti-feature.

In our present context, most mainstream languages have already handed out shared mutation. To my eye, this is the main reason so many languages have issues with writing asynch/parallel/distributed programs. It's also why Rust has an easier time of it, they didn't just hand out shared mutation. And also why Erlang has the best time of it, they built the language around no shared mutation.