> and many of them can't be fixed... And the boxing with C# unions can and will be addressed later
No, they won't. C# already got itself into a corner with 32 bit arrays and 32 bit spans. And if unions are introduced as reference only that will never be fixed due to binary compatibility requirement.
The new C# unions are not reference-only. The attribute/interface allows implementing custom union types by writing `TryGetValue`-methods instead of a single `object? Value {get;}`. The compiler handles this transparently.
No, they won't. C# already got itself into a corner with 32 bit arrays and 32 bit spans. And if unions are introduced as reference only that will never be fixed due to binary compatibility requirement.