> Having the state mutable would also need some kind of locking between the render view and updateState method

That's right, but that's exactly the main strength of Rust : the borrow checker deals with that locking at compile time with zero runtime overhead.

Not arguing on the other points though.

> Having the state mutable would also need some kind of locking between the render view and updateState method

You may want to brush up on Rust, the language has been designed explicitly to deal with these kinds of situations.

You're certainly right that in the mutable Rust land you don't have rewind/replaying state out of the box.