Of course it's a patch :)

Here's an update:

Even with the posted patch that allows the build to succeed, not all FS tests succeed, in particular zfs_test. It fails with a TIME_FAIL error (which is probably benign as it appears to concern a subsecond difference). 

I thus had to disable the build checks in order to be able to build my .deb packages.

Worse, update-grub2 will not generate a proper grub.cfg for ZFS roots: 

{{{
menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-b927688a3f8a6e13' { 
recordfail 
load_video 
gfxmode $linux_gfx_mode 
insmod gzio 
insmod part_msdos 
insmod btrfs 
set root='hd2,msdos4' 
if [ x$feature_platform_search_hint = xy ]; then 
search --no-floppy --fs-uuid --set=root --hint-bios=hd2,msdos4 --hint-efi=hd2,msdos4 --hint-baremetal=ahci2,msdos4 2def3c9f-2a12-41e0-911f-7de7cc142a99 
else 
search --no-floppy --fs-uuid --set=root 2def3c9f-2a12-41e0-911f-7de7cc142a99 
fi 
linux /vmlinuz-3.13.9-ck1-kubuntu-ck-amdf10-rjvb root=ZFS=zPatux/ ro 
initrd /initrd.img-3.13.9-ck1-kubuntu-ck-amdf10-rjvb 
} 
}}} 
In other words, the required zfs modules are not loaded, and the kernel isn't informed about the fact it's booting off ZFS. A more correct entry should read: 
{{{ 
menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-b927688a3f8a6e13' { 
recordfail 
load_video 
gfxmode $linux_gfx_mode 
insmod gzio 
insmod zfsinfo 
zfs-bootfs ($root) bootfs 
insmod part_msdos 
insmod btrfs 
set root='hd2,msdos4' 
if [ x$feature_platform_search_hint = xy ]; then 
search --no-floppy --fs-uuid --set=root --hint-bios=hd2,msdos4 --hint-efi=hd2,msdos4 --hint-baremetal=ahci2,msdos4 2def3c9f-2a12-41e0-911f-7de7cc142a99 
else 
search --no-floppy --fs-uuid --set=root 2def3c9f-2a12-41e0-911f-7de7cc142a99 
fi 
linux /vmlinuz-3.13.9-ck1-kubuntu-ck-amdf10-rjvb root=ZFS=zPatux/ ro boot=zfs $bootfs 
initrd /initrd.img-3.13.9-ck1-kubuntu-ck-amdf10-rjvb 
} 
}}} 
but even that gives an "invalid label" error upon boot and then tries to import the default pool name, rpool, instead of the right one. 
For reference, here's a menuentry from a different system (using the exact same kernel) which boots OK: 
{{{ 
menuentry 'LinuxMint GNU/Linux' --class linuxmint --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-7c11ad880751a42a' { 
load_video 
gfxmode $linux_gfx_mode 
insmod gzio 
insmod zfsinfo 
zfs-bootfs ($root) bootfs 
insmod part_msdos 
insmod ext2 
set root='hd0,msdos7' 
if [ x$feature_platform_search_hint = xy ]; then 
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos7 --hint-efi=hd0,msdos7 --hint-baremetal=ahci0,msdos7 39ff79e1-e153-490f-b302-4ba8e71fe643 
else 
search --no-floppy --fs-uuid --set=root 39ff79e1-e153-490f-b302-4ba8e71fe643 
fi 
linux /vmlinuz-3.13.9-ck1-kubuntu-ck-amdf10-rjvb root=ZFS=Patux/ ro boot=zfs $bootfs 
initrd /initrd.img-3.13.9-ck1-kubuntu-ck-amdf10-rjvb 
} 
}}}

And finally, even when I import the right pool at the GRUB prompt and get the boot process to continue, it will halt (freeze, block) during the initial systemd run, typically during or just after mounting the initial encrypted disks. If I disable that systemd entry, the process will freeze during network initialisation. Ctrl-Alt-Del will then no longer allow the system to be rebooted.