Yeah I think if it hadn’t been for the combination of Oracle and CDDL, Red Hat would have been more interested in for Linux. As it was they basically went with XFS and volume management. Fedora did eventually go with btrfs but dints know if there are are any plans for copy-on-write FS for RHEL at any point.
It’s not like Red Hat had/has no influence over what makes it into mainline. But the options for copy on write were either relatively immature or had license issues in their view.
Their view is that if it is out of tree, they will not support it. This supersedes any discussion of license. Even out of tree GPL drivers are not supported by RedHat.