I mean, I appreciate the huge engineering and design challenges here, but C# had non-null value types in 2002. It had generic value types in 2005 and it gained not-null “types with identity” in 2019 and no-one has batted an eyelid. (Indeed the type system support for value types still includes stuff Java isn’t even considering yet.)

Saying the mental model is too hard is basically saying your userbase is stupid. This stuff is not tricky.