The current situation (importing ByteString or Text for
  performance) is pretty good IMO. Haskell doesn't have Map 
  or Set or anything in the prelude, so I think it's 
  reasonable to leave powerful packed text types out as well.

Interesting. Maybe all we have is a community problem then? Since `String` is right there, and `Text` is both an additional dependency and an import away `String` gets used in situations it shouldn't.

  Try going to a python or java developer and telling them
  "array access should return an optional type instead of
  throwing an exception on out-of-bounds".

Alright, I think we have synthesis. From a Python programmers perspective the Prelude issues are somewhat trivial. From a Haskell programmers perspective it's offensive to good engineering. So it depends on your perspective:)