An excellent question. My impression could be mistaken, but to me this pitch comes off a bit like a piecemeal attempt to “do something about ownership” without filling in the complete picture. Swift didn't include non-copyable types in its original design for understandable reasons, but now that design gap is beginning to cost the language a lot (in particular, it is an obstacle to complete C++ interop), and because it is a fundamental piece of the object model. IMO it needs to be addressed holistically.
@Alvae and I have been working on a language design that could serve as the basis for a holistic approach to ownership for Swift, if anybody's interested in that.