I'm not knowledgable enough in that area, but as far as I know the OS X root needs to be HFS.
I can only answer by similarity: to boot from Btrfs in ArchLinux you'll need to load kernel modules in the bootloader.
Two reason:
1. btrfs isn't "built in" and needs to be loaded.
2. the boot loader needs to be able to read btrfs (obvious, but mentioning for the sake of mentioning)
That's doable for btrfs/Arch because we can put our own bootloader with btrfs compatability in.
Which leads me to my speculative answer:
No. It might be possible with a third party bootloader (iBoot comes to mind), but to have Apple adopt the OpenZFS implementation, or to revive their own, seems unlikely.
My guess would be that they are working on something, mainly because they have to find an alternative. Other people have talked about this being a necessary next step for Mac for years, but it does seem plausible that its in the works.
Replacement for HFS+ - ZFS? Probably not. Something else? Maybe WWDC 2015-2016.
EDIT: In case you mean full-featured as in "ZFS full featured", then yes, that's already there. Not Oracle full-featured, but ZoL (ZFS on Linux port) and somewhat IlluminOS compatible.
