Canonical announced that the 16.04 release of Ubuntu would include ZFS.
So What’s the Problem?

In one word, licensing.

Ubuntu is licensed under the GNU General Public License. ZFS is released under the Common Development and Distribution License.

According to Richard Stallman, creator of the Common Development and Distribution License and founder of the GNU movement, these license are incompatible. Stallman stated, “Code under GPL-incompatible licenses cannot be added, neither in source nor binary form, without violating the GPL.”
Stallman is not alone in this opinion. The Software Freedom Conservancy said the following in a statement:
Conservancy and the Linux copyright holders in the GPL Compliance Project for Linux Developers believe that distribution of ZFS binaries is a GPL violation and infringes Linux’s copyright. We are also concerned that it may infringe Oracle’s copyrights in ZFS.