Here's his reasoning: "honestly, there is no way I can merge any of the ZFS efforts until I get an official letter from Oracle that is signed by their main legal counsel or preferably by Larry Ellison himself that says that yes, it's ok to do so and treat the end result as GPL'd. Other people think it can be ok to merge ZFS code into the kernel and that the module interface makes it ok, and that's their decision. But…
That's his reasoning for not merging ZFS code, not for generally avoiding ZFS.
See also https://www.kernel.org/doc/html/latest/process/stable-api-no...
(fuse is a stable user-space API if you want one ... it won't have the same performance and capabilities of course ...)