QuantifiedConstraints and principal types

This is not a bug but I am trying to understand the ~~implication~~ significance of -XQuantifiedConstraints.

OutsideIn(X) (section **2.4**) tells us test actually has a principal type when we have implication constraints)

data T :: Type -> Type where
  T1 :: Int -> T Bool
  T2 ::        T a

test :: (a~Bool => b~Bool) => T a -> b -> b
test (T1 n) _ = n > 0
test T2     r = r

that subsumes

test1 :: T a -> a -> a
test1 = test

test2 :: T a -> Bool -> Bool
test2 = test

Now that we have -XQuantifiedConstraints does this change the story at all, if not you can close this..