This kind of comment kind of misses the point. The monadic style of threading error values is perfectly compatible with imperative programming if only language designers knew about it.
I love monads (I love arrows more, but that's another issue). I'm a language design geek. My level of expertise is different from someone who has just been hired into a new job and wants to get things done.
I suspect that most language designers know about monads - I'm not sure Rob Pike did, but it's pretty common knowledge among folks who do this stuff. Until you can explain them to the folks who'll be using the language in a way that doesn't make them seem like arcane black magic, though, you'll find programmers will just say "I don't get this" and use what they're familiar with.
No you don't, this is exactly what you don't need to do. Do we explain the finer points of stream implementation to would-be C++ programmers? No, when they need to do something non-standard with a stream/monad, that's the time to talk about them. For the majority of programmers it's just "when you need to write to a file you do it like this".
The dangerous part of Haskell, like Scala and C++, is that it also has super scary dark magical parts.