But think about what your asking.. Your asking to make a license that is _more_ restrictive then what is possible under copyright law. Is that approach really something you want to do when making 'Free' software?
The GCC folks probably really really need to reevaluate their entire attitude towards preventing proprietary plugins and back-ends/front-ends.
What is happening, it seems to me, that they are going to such lengths to fight a phantom menace that they are hurting real progress. That in a effort to combat a proprietary threat that, so far, has not existed, that they are doing REAL and immediate damage to the Free software folks that depend on their software and want to extend it to improve the state of the art.
Why not do everything you can to facilitate and create the best, most flexible, and most beneficial compiler you can and IF proprietary software becomes a problem THEN do something to try to deal with?
I am not saying that they should abandon all hope and embrace proprietary extensions.. I am saying that if people can prove a real benefit to extending the GCC framework in a way that would benefit Free software then they should do it.