I have a feeling most of this is over my head... but I start wondering about the implications for other free software projects that implement existing APIs, whether Samba and CIFS, or (a few years back) StatusNet and the Twitter API, Wine and Windows, LibreFM and Last.fm, etc etc. Not to dwell on specific examples, but just to point to the broader pattern: free software often re-implements APIs used by proprietary software when providing alternatives.

It's very common for free software (which often happens to be copyleft) to reimplement APIs used by proprietary software.

So...  “if there is even a modicum of evidence that direct textual copying occurred, then the alleged infringer must pass an extremely high bar of affirmative defense to show infringement didn't occur.”

Even if there's something good for copyleft *enforcement*, might it not be bad for a lot of copyleft software at the same time? In particular, free software (much of which is copylefted) that seeks to reimplement APIs used by proprietary software?

(Or, maybe you're simply saying that you are supportive of that statement on the high bar defense when there's evidence of direct copying, but that you disagree entirely that there's actually any evidence of direct copying in this kind of situation, given that it's a straightforward reimplementation of an API, etc.?)

I'm very hesitant to imagine any good coming from this decision...