I did a smoke test of Stackage Nightly's libraries [1] this afternoon using GHC 8.2.2. Only two libraries failed to build: extensible-0.4.5 and protolude-0.2, due to a change where type signatures like `foo :: forall k. forall (a :: k). ...` no longer compile without enabling TypeInType.
I only mention this because the migration guide for 8.4 [2] currently gives the impression that this TypeInType change won't land until GHC 8.4. This doesn't appear to be case, though!