Open Source Ruling Confirms Enforceability of Dual-Licensing and Breach of GPL

That seems to strongly contradict your "it plainly is not" claim.

As for GPLv2/CDDL incompatibility being "nonsense", I suggest you re-read the above. They are incompatible. The questions are:

- How much do the kernel devs care? They're the only ones in a position to complain, since as you say it's the GPL on their code being violated. The answer seems to be "not much", since CDDL is "in the spirit" of the GPL.

- How much would the legal system care if a complaint was made? As that SFLC link says, probably "not much", since it seems hard to argue that much/any physical or economic damage has been done, or any malicious intent (again, it preserves the "spirit")

- How much do Canonical care about the damage of a possible complaint? Clearly not enough to stop them going ahead.

- How much do users care about Canonical's risk-taking? Most users probably don't care.

I can imagine some 'enterprise level' (potential) customers who may run at the sight of "potential lawsuit", despite the "potential" seeming to be low, and the fallout from such a lawsuit being pretty insignificant (as SFLC says, since there's no malicious intent, it would probably just require a switch to Debian's model going forward, which would cause a little disruption but no real damage)

So, all the ZFS on Linux users are okay until Oracle sees money in suing them.

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".

In the US, (1) you can't let an issue get bigger simply so you can claim more damages the way SCO tried; and (2) when there's a specific statute of limitations -- like there is with copyright -- courts are less likely to say somebody delayed filing suit for too long, unless they made statements about trying to make a record to qualify for more damages, the way SCO did.

In the US, it used to be possible to lose copyright if you failed to enforce it, but that hasn't been the case for decades.