the announcement of the true-name package is pretty funny

That's exactly the deal with .Internal modules, but it's social convention and comments rather than a language keyword. I prefer it this way, frankly, as we also have .Unsafe, or .ThisIsWrong, or what have you, which strongly encourage some consultation of the documentation to understand the many facets of the world of pain you are stepping into.

When it's solely a matter of a library that you are maintaining and someone somewhere else unaffiliated with you is breaking the invariants to their own ends, that's fine, what they are doing is irrelevant and if something goes wrong it's only their headache.

But if you both work for the same organization, and you build something and take the time to ensure there are invariants that hold, they're probably important and your code may in fact need them to hold to make sense. Then someone else comes along and rips apart the internals and changes with things to make their code work in a very hacky and un-haskell-like fasion, and returns data to you with the invariants you so carefully preserved all violated and your code is now apparently broken. Now you have a headache.

Remember, 90% of everything is crud, including programmers and even co-workers. Much of Haskell's power comes from the kinds of invariants you can guarantee, not from pretty please asking people not to break them unless it's really convenient.