Neil McGovern has written a blog post today explaining that work is still ongoing for landing ZFS support in Debian. This ZFS file-system support will be added to Debian's contrib repository and will be a source-only, DKMS module. In other words, due to licensing issues, they will not be patching their default kernel package or the like, but rather will distribute it as a source package that will then build locally on the user's system against their installed kernel version.
More details on the Debian work going towards ZFS can be found via this blog post. Meanwhile, Ubuntu is also working on ZFS for 16.04 LTS. If you want to try the ZFS file-system on the distribution of your choice, visit ZFSOnLinux.org.