Can be used for empty data decls such as Void. Proposed syntax is to leave off the of keyword.

data Void

absurd :: forall a. Void -> a
absurd = case _

Type inference may suffer. What would the inferred type of absurd be if no explicit type was given?

Issue about exhaustiveness checker exists elsewhere.

Not a breaking change, but existing code that uses data X as a short-hand for foreign import data X :: Type must be modified to use the latter; an empty data declaration is now truly an empty type.