It's orphaned in Debian as well, but I'm not sure what significant advantages it has over btrfs, which is very stable these days.
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Also see https://www.phoronix.com/news/Josef-Bacik-Leaves-Meta
Now you've piqued my curiosity; what uses that many filesystems/subvolumes? (Not an attack; I believe you, I'm just trying to figure out where it comes up)
The main criticism in this thread about btrfs involves multidisk setups, which aren't relevant for me, since I'm working on cloud systems and disk storage is abstracted away as a single block device.