Depending on an out-of-tree module can get pretty crappy on Linux. The upstream kernel will break you a lot. If your distro is on top of keeping your out-of-tree feature working then great. It gets messy whenever that is not the case and/or suddenly you want a driver or feature only available in a newer kernel.
Larry can't change the fact that GPL is the source of incompatibility - the general interpretation is that GPLv2 forbids code that has stricter licensing terms than GPLv2, and CDDL happens to have that - in form of patent grant.
It's also why GPLv3 code has a license issue with Linux kernel, which is GPLv2.
There are probably other options, too.
It's a pipe dream anyway, of course.
Another is that all the porting work in ZoL that isn't already GPLv2 is CDDL - and Oracle is not the copyright owner. In fact, the copyright owners would not want to change the license to GPLv2, unless maybe it was done as dual license.