1) UK law should not be generalized worldwide. 2) The writer of the license has no special powers to interpret, enforce, or guard code licensed under that lice

1) UK law should not be generalized worldwide. 2) The writer of the license has no special powers to interpret, enforce, or guard code licensed under that license. They can express strong opinions, which (if it's a well written license) garner attention, but they don't have any actual legal rights in the matter. Only the copyright holder (or someone they've delegated their rights to) can bring suit. 3) Even if the rights are estopped due to being left unenforced, if you go out tomorrow, contribute some code to the linux kernel, and then wait for canonical to link that with ZFS, you would almost certainly have your own right to bring suit. You're not estopped by someone else's failure to enforce their own rights, independent and unrelated to yours. In any case, the arguments over ZFS have always boiled down to a few technical incompatibilities between the GPL and CDDL, mostly centering around some patent licensing clauses in the CDDL. While plenty of parties theoretically have standing to sue, in practice the Linux folks would love to merge it if they could, as would the OpenZFS authors - with the notable potential exception of Oracle, who remains silent on the issue. As such, none of the open-source developers are suing to enforce any sort of technical licensing problem because it's not in their interests to do so. And if Oracle gives up some rights, well, that's a good thing, right? In short, most everyone involved doesn't want there to be a lawsuit - and so there isn't. And that's not a bad thing. The problem the FSF/SFLC keep going on about is that there's a lot of uncertainty - i.e. "someone _could_ cause you a lot of trouble by suing, so please stop doing this before you get yourself or your customers sued by someone else".