>The problem is that no one really knows what constitutes "safe" use of GPL
Outside of a business that can hire lawyers, it would be helpful for the FSF and sites like http://opensource.org/licenses/BSD-3-Clause to have examples right beneath the licenses. Something like: "Here is a JS plugin with BSD-3 here is another plugin based on it. Note how the license did/didn't change." "Here is an MIT license and an example of a company adding that code to their app with license intact on the app's about screen". Stuff like that. http://choosealicense.com/ is helpful, and part of the way there.
> Outside of a business that can hire lawyers, it would be helpful for the FSF and sites like http://opensource.org/licenses/BSD-3-Clause to have examples right beneath the licenses
They can't do that. The law doesn't work like that. The GPL FAQ[1] has to be deliberately vague about some things, because judges and juries themselves are vague, as are the laws they work to interpret. You can't have cut-and-dry examples of what can be done and what can't, because there can be many other externalities that could make a different case work in a different way, despite similarities to your proposed list of examples.
There are can be broad strokes, but the law is not a programming language. Recent xkcd comes to mind.[2]
The organizations with lawyers behind them won't, and quite can't, do it. They're not supposed to give legal advice in general terms, no one is.
Now, if individuals would be willing to work together to put up such a site, as a collection of information and opinions, with necessary disclaimers so that its limits are well-understood, and add examples, thoughts about them, critique and disagreements about them too, that would be different.
Outside of a business that can hire lawyers, it would be helpful for the FSF and sites like http://opensource.org/licenses/BSD-3-Clause to have examples right beneath the licenses. Something like: "Here is a JS plugin with BSD-3 here is another plugin based on it. Note how the license did/didn't change." "Here is an MIT license and an example of a company adding that code to their app with license intact on the app's about screen". Stuff like that. http://choosealicense.com/ is helpful, and part of the way there.