Hello, everyone! Today, I finally migrated from ZEVO to OpenZFS 1.2.7, and it was totally seamless. All I did was shut down my old ZEVO system, unplug the disk array, plug it into my new Mac Pro running 10.9 (with Mavericks installed), and then run "sudo zpool import tank". Done!
Not only did it just work, but disk performance has improved dramatically. I'm (now) happily on a Mac Pro running Mavericks 10.9, talking to a 8 x 4TB Areca Thunderbolt enclosure and getting about 1.4 GB/s read and write—at least, using Black Magic's Speed Test, which I'm told might not be the best test (about 3x what I was getting on 10.8 and ZEVO).
Congratulations—and, thank you—, developers and community supporters, for making this work for those of us who are not actively contributing code!