[AndrewDucker]

Yes, but see the section on custom unions* - you can write non-boxing unions/generators.

* https://devblogs.microsoft.com/dotnet/csharp-15-union-types/...

[mwkaufma]

Yes, there's a compat-shim in the stdlib/runtime, but not in the language syntax. E.g. it by-definition won't do escape-analysis and optimize discriminated value-types with the first-class keyword.

[Izikiel43]

For now