I agree. Tight, stateful algorithms aren't going to disappear and are harder to reason about (currently) in functional languages. I expect that their implementation and use will shrink over time, in the same way that embedding inline assembler has all but disappeared.
I definitely don't expect, or hope, that monads are the final answer to isolating state manipulations, and I agree with a later comment of yours that the IO monad is not granular enough as it is in Haskell. When a large chunk of code ends up being written in the IO monad or in another monad that wraps IO, you miss out on a lot of safety and reasonability that Haskell is supposed to give you. And I've seen that happen (my own projects included).
I definitely don't expect, or hope, that monads are the final answer to isolating state manipulations, and I agree with a later comment of yours that the IO monad is not granular enough as it is in Haskell. When a large chunk of code ends up being written in the IO monad or in another monad that wraps IO, you miss out on a lot of safety and reasonability that Haskell is supposed to give you. And I've seen that happen (my own projects included).