Pretty much all the tools I've developed in the past couple of years for AAA games have been almost exclusively made with Python.
One of them we even developed tools to be DCC agnostic, which means that they could run both in Maya and 3ds Max flawlessly.
The usual GPL issue around plugins is whether program+plugin are a "mere aggregate" or a "derivative work". This doesn't really matter if they aren't distributed together, but even if it did, the question is no easier to answer in the case of interpreted vs compiled code. They are still running in the same process, exchanging internal data structures through direct procedure calls. It just so happens that one is running through a translation layer.
If that translation layer protects you, then you could just as easily enjoy that protection by running binary plugins through a no-op emulator.
And regardless of all of this, there's no reason Blender Python plugins can't use Python native extensions for performance. FLIP Fluids, for example, has a C++ fluid sim engine and uses Python just for the interface to Blender.