I'm glad to see someone implementing these ideas.
This sounds similar to what I envisioned in Exploratory proposals: Pure & Concurrent. Except in my case I avoided completely the concept of a "value type".
I find it closer to reality to consider each type can sometime behave as a reference and at other times as a value. Case in point: a pointer can be treated as a value as long as you're not dereferencing it. An array of object references has value semantics if all you're doing is getting its count. What matters really is not the type or the data it stores, but whether what you do with it breaks value semantics or not.