NILFS is absolutely wonderful; it was very unfortunate that Linus chose to dub btrfs as the ext4 successor all those years ago, because it cut off a lot of interest in the plethora of interesting work that was going on at the time.

A decade later and btrfs is still riddled with problems and incomplete, people are still using xfs and ext4 for lack of trust, one kernel dev has a side hobby trying to block openzfs, and excellent little projects like nilfs are largely unknown.