[dragonwriter]

> Why not just write the license in such a way that linking against the stable ABI requires your code to also be GPL licensed?

Well, for one thing, its dubious than ABI's are copyrightable (for much the same reasons as that is true for API's, see Oracle v. Google), so work derived from an existing products ABI quite likely doesn't need a copyright license, so therefore is unlikely to be effectively restrictable by way of a gratuitous copyright license.