would it be possible to implement a way to use reflink for mariabackup on filesystems which support it like btrfs and xfs?
The benefit of this woud be that, on systems where the database is installed on a filesystem with reflink-support, the backup could be done within parts of a second without the need of additional space no matter how big the database is (and if the backup-destination is on the same filesystem). On systems where the local backup is only used temporarily until it gets uploaded to a backup-store this is absolutely fine and can save a lot of I/O and time.
You can even use this to "clone" a database e.g. for testing purpouse without the need of additional space (backup a single db and restore it with a different name using cp --reflink during restore)