if its under GPL couldn’t they be forced to disclose the source code?
What, where do you get that? Any publicly conveyed copies of gpl-licensed software must make their source code available, and be published under the same license. This is true regardless of modifications.
I could be wrong and I’m more then welcome to being proven that. But wouldn’t this be like asking me to redistribute the whole process of running ZSNES on linux? Seems pretty infeasible.