I think this article exaggerates the potential licensing problems. There are few GPLv2-only apps, it's common for app developers to make license exceptions (especially in such an inoffensive case as GPLv2+Apache), and none of that would prevent other apps from using GCD.
Yes. For example back in the days Mozilla wasn't dual MPL/LGPL licensed, the Galeon web browser contacted all contributors to modify the license to explicitly allow linking to gtkmozembed, the Mozilla renderer for GTK.
The hardest part is contacting all contributors. But once you've contacted them, people rarely object to adding a linking exception.
Here's hoping some useful Linux uses can come out of this - packet-based multithreading seems like a useful abstraction to me, though I am an admittedly inexperienced in multithreaded programming outside of class.
Does anyone know of any major GPLv2-only apps out there that would provide a major roadblock to porting this to Linux?