Its nowhere near ZFS/HAMMER/BTRFS ...

Check their FAQ here: https://stratis-storage.github.io/faq/

In short:

In terms of its design, Stratis is very different from ZFS/BTRFS, since they are both in-kernel filesystems. Stratis is a userspace daemon that configures and monitors existing components from Linux’s device-mapper subsystem, as well as the XFS filesystem.

Red Hat move seems very strange here because it would be better just to hire several BTRFS developers and join the BTRFS Linux ecosystem instead of writing something new ... I still do not know what for ...