You might be aware of this but FreeBSD has all of those features that you mention. The objections that you have against Solaris might still apply though.
I've also thought about FreeBSD and while pkgng is really great it's a similar problem.. I'm stumbling upon bugs or untested things and I'm unable to contribute time to fixing them.
I don't run anything big on FreeBSD and ZFS. I have not experienced problems on a raidz2 ZFS fileserver that runs FreeBSD except that disks drop out quite randomly but I've yet been unable to pinpoint that and it's likely that these are hardware issues as the system runs on budget hardware.
Sorry if my comment spreaded FUD.