I wonder if one of the most important changes is pure nomenclature: the updated type definition keywords. In prior versions the "obvious" way to define a type g

I wonder if one of the most important changes is pure nomenclature: the updated type definition keywords. In prior versions the "obvious" way to define a type gets you a mutable type, and going forward the obvious way gets you an immutable type. Of course this doesn't change what the language is capable of, but I hope/expect it'll encourage better practice.