Why would Oracle have to add Btrfs support back into the RHCK? It's exactly the point of this kernel to be 100% identical to upstream RHEL. If an Oracle Linux user needs Btrfs support, it will still be included in the "Unbreakable Enterprise Kernel" (UEK), which Oracle provides as an alternative.
Does Oracle support Btrfs (as opposed to making it just a tech preview) with the compatible kernel? I don't think so, since it's the same code as RHEL. And if not, hosing in-place upgrades is acceptable. RHEL 7 is supported until 2024.