@elovin Welcome to the Rockstor community.
As btrfs is ‘as standard’ in upstream kernels and has been for a number of years we should be OK with our continued use of elrepo’s mainline kernel.
Hopefully the rest of your questions should be addressed in our first thread from back when this was announced. Please see:
And later we had another thread started on the same question, linking for convenience:
The short of it being that they never actually supported btrfs and we never used their ‘technical preview’ variants (kernel or user-space wise) as they were simply too old. The CentOS kernel is only used during the installer, once the installed system is booted it uses the far more modern and generic elrepo mainline along with appropriately compiled btrfs-progs.
Hope that helps and thanks for the enquiry.