I don't know and I don't really care if it was always the plan or is a result of feedback. I think this is very good news.
I think that this means that it will be copy on write behaviour so that if you aren't changing the array you get pass by reference performance and only pay the call by value price when a mutation will occur. It may even be smart enough to know when the caller isn't going to access the array again and allow it to pass and mutate the original. We'll see in beta 3 (or maybe later).Update: I've added a new post about the changes.