The ZFS comment in the document  is time inspecific. It's got version 1.0 in 1st half of 2018 and the "rough ZFS feature parity" comment is not until version 3.0, which has no listed time frame.
This is going to take lot of work, and not just for the stratis developers but for projects that need to manipulate it. It's asking for a lot of work for bootloader projects to support it, and
SUSE has succeeded in shipping atomic OS updates and rollbacks by default both for enterprise and community versions of Linux several years ago. Facebook is using it, and the usage is growing.  And there are any number of examples of production usage of Btrfs at scale if you go look for them.  And the good and bad are fairly well understood, it is in fact getting better and will continue to get better. And Red Hat isn't waiting. 
What you're going to find in storage is that there are multiple valid approaches, no clear one size fits all winner, and people will choose based on the tools they're familiar with, the company they trust, and their use case. I pick Btrfs over ZFS pretty much based on equivalent trust and better flexibility for my use case, but then I'm much more familiar with Btrfs tools and where the bodies are buried than I am with ZFS. I don't need to go around impugning other projects to justify what I use.
Unsurprising. Red Hat has not hired upstream Btrfs developers for years, where SUSE has hired bunches. Meanwhile Red Hat has upstream ext4, XFS and LVM developers.
If you're going to support a code base for ~10 years, you're going to need upstream people to support it. And realistically Red Hat's comfortable putting their eggs all in the device-mapper, LVM, and XFS basket.
But, there's more: https://github.com/stratis-storage/stratisd
Btrfs has no licensing issues, but after many years of work it still has significant technical issues that may never be resolved. page 4
Stratis version 3.0 Rough ZFS feature parity. New DM features needed. Page 22 https://stratis-storage.github.io/StratisSoftwareDesign.pdf
Both of those are unqualified statements, so fair or unfair my inclination is to take the project with a grain of salt.