A GPL-enforcement suit against VMware

There is no constraint of API compliance in this case, as VMware wrote it themselves. Designing something like that is creative work and thus falls squarely within copyright.

However, I suspect (but didn't investigate further!) that *this* API is merely a convenience layer which defines an arbitrary boundary between GPL'd and closed-source code.

The kernel is licensed by the GPL and not the LGPL, so this is not sufficient as per the authors' intent. Intent tends to matter to German courts.