As for cgroups blkio - there is already a bug report: https://github.com/zfsonlinux/zfs/issues/1952
Sorry. It was not my intention to suggest that ZFS does not compile on new kernel versions. I've never had problems with that. I just wanted to point out that it's not in the mainline kernel and for some people that might be important.
Thanks for your great work on ZoL! It made my life a lot easier :)
As for the issues you linked, the project will likely not be able to tackle them until next year, but being in the tracker means that they will receive attention.
WRT to Gentoo, Gentoo does have a tool called genkernel that I consider to make such upgrades fairly easy. It can handle any of initramfs generation, kernel compilation, kernel configuration and bootloader configuration (GRUB2). However, it does have a moderate learning curve. I am also one of the genkernel developers, so I likely have an implicit advantage over users in understanding genkernel. In particular, I find some users have difficulty discovering its functionality, despite it having things fairly well documented in the man page. There is likely more that needs to be done in this area.
To expand on your LZ4 comment, LZ4 is 3 times faster than LZO at decompression:
https://code.google.com/p/lz4/
However, LZ4's real innovation is on incompressible data. I do not have a reference at the moment, but there have been benchmarks on the userland lz4 tool on incompressible data that show it processing 10GB/sec. This is because LZ4 uses a hash table that enables it to give up when trying to compress data far sooner than other lempel-ziv implementations do.
As for stability, it is hard to for me to tell what you mean by that, but I just wrote a series of blog posts on the topic. If there are any outstanding issues not listed there, please file an issue on github:
https://github.com/zfsonlinux/zfs/issues/new
I also encourage you to file an issue requesting support for cgroup bsaed IO throttling. You are the first person to mention it.
As for not compiling with new kernels, the 0.6.3 release supports Linux 2.6.26 to Linux 3.16 while HEAD adds support for Linux 3.17 release candidates.
I briefly touched on the rootfs on ZFS issue in my blog post. I plan to add ZFS support to syslinux in the near future as per a discussion that I had with Peter Alvin at LinuxCon North America 2014. I expect this to resolve the issue for those willing to use syslinux as their bootloader.