One of the claimed benefits of .NET Core was that they could improve the runtime at a much faster pace than .NET Framework did, especially if that meant adding new features or even IL opcodes. And they've done this before, with a big one (IMO) being ref fields in ref structs. Lately, when it comes to developing C#, the language design team has frustratingly been trying to shoehorn everything into the compiler instead of modifying the runtime. Then they say the runtime should be modified to pattern-match what they output. If DUs are to be implemented fully in C#, niches would probably be impossible. This means Optional<T>, when T is a class, would take two words.