This isn't describing "post-functional", it's just plain old "multiparadigm". Multiparadigm languages generally have a "base" language type that is at least slightly preferred or possibly what everything else compiles down to, with the tradeoff that anything you can't get without being "pure" in some paradigm won't be available to you. In practice this is often a good choice.<p>Lisp, Python, C++, Perl, it's a pretty well-populated space and nothing in that article leads me to believe that there's any particular innovation in the paradigm arena there. That is not to say the language itself is good or bad, just that this article is based on a really weird premise.
I'm a little disappointed that the article suggests that the IO monad makes Haskell impure. While it is certainly true that unsafePerformIO violates purity(and type safety, as well), without it, IO is perfectly pure. It's just that if an IO a value happens to end up in main or something referenced from main, input and output happen. From the language's perspective, the IO monad functions could all be perfectly pure and have no relation to input or output(putStrLn could be a no-op, input functions could always return the same thing). It would be utterly useless for its intended purpose, but there would be no difference in terms of its purity.