> - "cut and paste and edit" is broken. You can't autoformat the pasted code into the right place, you have to go back and fix the whitespace. Since whitespace is semantically significant, this can introduce bugs.
Depends on how your editor is configured / it's feature set. Which makes me wonder how editorconfig would handle this when enabled. It seems like a insignificant issue to me, you can auto-PEP8 the code before pasting it. You should probably be following PEP8 anyway (as far as spacing is concerned at least).
> - visually identical whitespace may not be textually identical whitespace. Unless you go around breaking the tab key off your colleague's keyboards you'll trip over this. Especially (again) if you paste. Occasionally seen in merges too.
I turn on show all whitespace on my editors regardless of programming language. I've been burned by Sublime Text not just figuring out the already defined whitespace ruleset for a file by what it's using and just shoving in it's own defaults. I wish all editors would base whitespace on what the file's structure looks like, if there's mixed spaces, give me a warning.
> - editors can no longer give you 100% correct indentation.
I don't understand this, it sounds like you've got your editor configured poorly or something? But it goes back to how unintuitive the nice editors can be. You can use editorconfig to define the indentation project wide, then any editor should pick it up, of course if you define PEP8 at a minimum it guarantees spacing settings.
I'm not sure if PyCharm covers a few of those cases, since I use it so seamlessly I don't usually have complaints.