No, they literally cannot. The current OpenZFS codebase is the combination of the original Sun/Oracle-owned code and a massive number of new committers. Now, Oracle could relicense the original code, but they can't do anything about the later additions, because they don't own the copyright on those. The only maybe possible carve out is if the code is licensed with something like "CDDL 1.0 or later" then they could make a new version, but I'm not clear on whether that's an option or whether the code is licensed CDDL 1.0-only. IANAL, YMMV. (EDIT: Apparently the CDDL already has a version 1.0 and 1.1? So take exact versions with a grain of salt above.)

This is a myth that keeps coming up, in spite of being debunked time and time and time again. Solaris could not use the GPL because Sun didn't own the rights to all parts, so the GPL's copyleft wouldn't work and they needed a new license.

In hindsight, an explicit "GPL compatibility clause" like the EUPL has would clearly been a wiser choice, but that wasn't clear in 2005, and it's too late for that now, unfortunately.

On the other hand, you could also blame the GPL for not recognizing that other copyleft licenses exist; they also could have written a compatibility clause in GPL 3. "CDDL is incompatible with the GPL" could also be phrased as "GPL is incompatible with the CDDL".

Thank you for fighting the good fight out here in the wilds of the internet! It's so frustrating that the misperceptions on this seem to be uncorrectable -- and it's to the point that I have sadly concluded that the false narrative around this somehow being a CDDL issue is one that people actually want to believe because to know the truth would be to confront Linux's own NIH syndrome, which remains profound.

> I have sadly concluded that the false narrative around this somehow being a CDDL issue is one that people actually want to believe

Yes, I agree; there's a few other topics like this. I call this "hacker conspiracy theories", because at this point that's basically what they are.

I mostly comment on these things for the benefit of innocent onlookers, who were not yet around when all of this went down, and not to convince the person who posted it.