[p_l]

Oracle isn't copyright holder for OpenZFS. That's one part that OpenSolaris and OpenZFS projects managed to ensure. What Oracle could do was to close OpenSolaris again under proprietary license, something that Brian Cantrill IIRC blamed on the use of copyright assignment, and that open source projects should never use it - with that as a specific example.

OpenZFS devs have openly declared that no, they are not pushing to include OpenZFS into Linux kernel, and that separate arrangement is just fine, especially since it allows different release cadence and keeps code portable.

Mainly there's an issue with certain Linux Kernel big name(s) that like to use GPL-only exports (something that has uncertain legal status) in a rather blunt way, and sometimes the reasoning is iffy.