Currently, role annotations look like this:

data Foo a@N = ...

I've received several criticisms of this syntax:

• It is not backward compatible. If a library wishes to use role annotations and remain compilable with earlier versions of GHC, preprocessor commands are necessary.
• It is inscrutable for someone not well-versed in roles.
• It reminds people of as-patterns, which it is unrelated to.
• It is conceivable that it would conflict with type-level as-patterns.

For these reasons, I propose the following:

data Foo a {-# ROLE Nominal #-} = ...

This syntax, while verbose, eliminates these concerns, considering that the new syntax is easily searchable for someone who doesn't know it. I have proposed something similar on ghc-devs, with no response, so I will implement it shortly.