Wow - to say this is a major major result in an understatement. This is going to turn GPL litigation on its head, and allow more activist type folks to pursue cases aggressively. On the developer side I can see a move away from GPL - as adding third parties into this is going to be pretty unappealing for some developers.
I think historically distribution of source code was seen as a condition of the copyright license (which meant copyright holders enforced), not as a separate contract right available to third parties (which would mean users and other can go after a variety of claims).
I think historically distribution of source code was seen as a condition of the copyright license (which meant copyright holders enforced), not as a separate contract right available to third parties (which would mean users and other can go after a variety of claims).