Default What is the truth behind the sdcard complaints for KitKat

While researching the great N7000/Galaxy-S2 sdcard FUSE deadlock bug, I've come across lots of posts that complain in the strongest possible language about how KitKat has changed the rules for SD cards.

The android police thread named "external-blues-google-has-brought-big-changes-to-sd-cards-in-kitkat-and-even-samsung-may-be-implementing-them" seems to sum things up less emotionally:
  • An app without any permissions has automatic read and write for designated private folders on the primary and secondary storage
  • An app with WRITE_EXTERNAL_STORAGE, also has:
    • Read and write for any public folder on the primary (built-in) storage
    • Read (not write) for any public folder on the secondary (SD card) storage
This implies, as many posts point out, that some of our most useful tools (file managers, backup apps, ...) will no longer work.

But I'm not seeing that - FX, even in non-SU mode, can still create folders and files and copy between cards, for example.

So what IS the (full) truth, and how does this affect Omni?