Just out of curiosity, wouldn't it be able to setup thousands of ZFS test in a CI environment for every new linux development build, to see if there are any regressions, e.g. 1 failed, 999 passed.

Second thing, if more and more people start to use ZFS then it will automatically become a center of attention for linux kernel developers, because they don't want to break their users systems.

And one last note: not everything that is out-of-tree is automatically unstable, otherwise the whole userspace code would be unstable.