Stable yes, but no protection from bitrot, and the journal of ext4 is the band aid, instead of a cow fs like zfs or btrfs.

btrfs with its send/receive (incremental fs-level backups) is already stable enough for mostly everything (just has some issues with raid 5/6), and is much more performant than zfs. And it is also in the linux kernel tree (quite hugely useful). Of course, if more zfs-like functionality is what you look for.