The engineering problems are tractable even in those cases: Don't put the root file system on ZFS. Develop some kind of first-boot initrd that includes enough of a toolchain to build zfs.ko. I'm sure there are other, better ways to solve shipping ZFS in a virtual machine image, especially compared that to the legal and business risks of having a LTS release deemed a copyright infringement: Court costs, legal fees, fines, re-releasing Ubuntu, etc.