That would be very controversial, in that Swift deliberately does not support default values for types (and in the general case a type doesn’t need to be constructible by the user at all).
There’s no get (or set) accessor for subscripting Vector—the semantics of accessors necessary for supporting noncopyable elements are being pitched separately.
It’s not mentioned at all in this proposal, probably for that reason, but you do make a good point that it is impossible to understand what’s going on for the purposes of proposal review without any reference to something about it.