You can already install on ZFS in FreeBSD.
I've been running FreeBSD on my home server for about a decade now -even before ZFS- and have loved it. But I used to run Linux VMs on top of it. However it's only recently that I've decided to go fully FreeBSD on it, using jails instead of hardware virtualisation. I honestly can't understand why I waited so long to do so. It's proven to be a far more elegant solution for what I needed.
While I do still run Linux on my desktop and work with Solaris and linux as my day job; FreeBSD seems a vastly overlooked alternative these days, which I think that's a great pity. its stable, proven and dead to administrate. But each to their own I guess.
I bought it about 5 years ago for a whopping $99, but it has an issue with shutting down about 30 to 50 seconds after POST.
I figure that I got my $99 worth out of it, and have acquired a new HP Envy 15, which is, unfortunately, equipped with a Broadcom 4313 wireless adaptor, thus I haven't yet taken the time to attempt getting the WiFi card to work in FreeBSD, but I intend to do so soon. (time permitting)
However even that aside, I couldn't see myself prefering OpenIndiana; FreeBSD is a very different kind of 'UNIX'. While SunOS does historically have some roots in BSD, it's still very much a SysV-style UNIX; and as much as I use SysV-like systems daily for work, my true love is for BSD.