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"You can use OpenZFS on Linux; the problem is building it into the kernel because Sun's Common Development and Distribution Licence is incompatible with Linux's GPL2. [ ... ] Btrfs is not so encumbered. "
Btrfs is released under the GPL, which mean it's MORE encumbered.
If things aren't compatible with the GPL because they won't adhere to it's restrictions, then it's the GPL that needs to change.
Similarly with ZFS, and the GPL zealots criticising it for not licensing under the GPL. If YOUR rules are stopping you from using something, it's YOUR rules that need to change, not the other parties.
Biting the hand that feeds IT
