Good luck. There is long road ahead. Both ZFS and Btrfs were initially developed by really high caliber people and experts with good track record. ZFS had five years for full time development until release, next five years to get close to the features and stability that ZFS has now. Btrfs started 10 years ago and it's still trying to catch up.
I think you think to highly of the btrfs group. There not bad people but Filesystems are HARD to get right and they simply are not in the same league as the zfs developers were. The well known raid 5 issue btrfs had shows a prime example that the btrfs simply is not in the same class as zfs' design. I wouldn't compare the two.
ZFS was started internally at Sun with a bunch of resources dedicate from people who had been involved in and thinking about storage devices and file systems and their myriad problems for a long time well before they started ZFS. And the cat wasn't out of the bag to end users for about 4 years, during which time there wasn't the contributor pile on effect.
Btrfs had to contend with some balancing act of not saying "no thanks" to patches, meanwhile those contributions very likely did clutter up the code every bit as much as allowing the contribution aided in hyping the project rather than turning people away from contributing at all.
As for raid56, ZFS emerged before cluster file systems like Ceph and Gluster were even conceived. The companies that need to store tons of data, and fund various storage related projects don't care nearly as much as they once did about raid56. They can just replicate the data elsewhere using Gluster and if a whole brick, be it XFS or Btrfs implodes, they can just make a new brick and the data gets replicated again.
Anyway, ZFS and Btrfs are really not comparable even though on the surface they seem to do really similar things.