Are you sure? I thought that ZFS for Linux can be distributed, but, only in source code form. So you would have to distributed the source code, then, build the ZFS module for it after / during installation.
As I get it, ZFS core (as necessary for GRUB to read the filesystem) is available under GPL. While not enough, this could've been a starting point.
However, the main issue is ZFS is also patent encumbered, so re-implementing (even with clean-room approach) it may mean meeting with Oracle's lawyers.
That's sad, considering btrfs still suffers from internal fragmentation issue, as Edward Shishkin had shown in 2010.
That's pretty much it, except that nobody big has actually tried doing that (distributing an install CD which specifically builds ZFS as part of the standard install process), therefore it's not been in courts, therefore it's not proven that it's legally safe to do so, therefore anyone larger than a small business is unlikely to build on top of it.
