The User Guide comment says this is not allowed, but the explicitly bidir form is

pattern StrictJust a = Just !a

pattern StrictJust a <- Just !a where
  StrictJust !a = Just a

Given that the compiler splits an implicitly bidir form into two separate artefacts anyway, is there some deep reason I can’t go

pattern StrictJust !a = Just !a
--                 ^^ parse error here

and get the compiler to turn it into the explicitly bidir form for me?