My reading of the GPL is that if you are the rights holder of some software, and there is a xGPL licensed plugin to said software, you can only distribute changes to the plugin if you also distribute your software as xGPL. In other words it is impractical for you to make changes to xGPL licensed plugins to your software.
> Many companies will instead do shim/bridges that aren’t GPL themselves but something like MIT. The bridge talks to proprietary code and the GPL but doesn’t bridge the license over as a result.
I'm fairly sure this is not legal, see https://www.gnu.org/licenses/gpl-faq.en.html#GPLWrapper
The point is there is too much in the GPL that is open ended and can only be known for sure after litigation.