You’re making your programs orders of magnitude slower to the back of claims that have absolutely zero metric demonstration.

>simplifies a lot of things

Runtime immutability simplifies nothing.

>avoids common problems related to concurrency

While simultaneously creating new problems. Like fine, you cannot make an edit on an object out from under the rug of another thread… except that in most cases, you have now just made that old object into invalid state that is lingering around your program like a death trap and to get around this, you are forced in to some pretty terrible synchronization bullshit that just locking objects doesn’t suffer from.

>Implementing CoW is not too difficult

The single greatest predictor of defects for every single language ever is “lines of code”. Implementing CoW sounds straight forward, but actually, incorrect CoW is a common source of bugs and you are just hand waving that away.