Incidentally, some of these things work on Ubuntu: superpages, zfs, and clang. & I wouldn't call Journalled Softupdates an advantage, more of a catch-up to the various journalled filesystems supported by Linux.
The license doesn't allow to distribute a binary build of it, but you can build your own rpm and deb packages and install it to your own servers.
(According to their FAQ: "In a nutshell [...] This means that a single derived work of the Linux kernel and ZFS cannot be legally distributed."
Honestly, besides some quick tests I don't have any experience to judge how stable it is, but definitely better than the fragile fuse setup you are mentioning.
I found softupdates to be superior to traditional journaled filesystems for boot filesystem - BIOS can't replay the journal, but softupdates provide always consistent fs state on disk, so kernel and modules can be loaded and booted. Only leaks of free blocks need to be fixed with background fsck if filesystem is dirty.
