Allow sealed interfaces without subclasses

[Jakob Brünker]

 Hi all,

While I like sealed classes a lot in general, it's lacking one simple
feature that prevents it from being used to fully emulate algebraic data
types: You cannot make an uninhabited  type (modulo null), since you cannot
have a sealed interface without subclasses.

Is there a good reason to disallow this? It does come in handy every once
in a while in languages where it's possible, especially when trying to
convince the type checker that a particular combination of patterns is
impossible. As a data point, in Haskell, this used to be impossible, but
was later adopted into the language standard, and in fact is used in the
standard library to define such a type under the name Data.Void.

Thanks,
Jakob