It seems like this relies for some of its safety guarantees on checks in (their fork of) the C# compiler. For example, owner non-copy guarantees seem to be enforced at the C# front end level rather than in the CLR. That could cause problems for getting it into CoreCLR (and much more so the desktop CLR), as this is meant to support multiple languages; relying on a specific language front-end for safe use of a feature feels at odds with the 'common language runtime' philosophy... It would be great to see it though!