The concept as proposed by Hoare is strictly necessary for things like partial relations

I read the 'Partial Functional Relationships' section. There's nothing special there. It's just structs with nulls.

Polluting every type with it I think you're reacting to the pollution of the syntax. Hoare already polluted the semantics: Every type can be null. You can't even model a NonNull<Spouse> because NonNull itself can be null.