Kent has admitted (many times) that snapshots are one of the more difficult features to add in a reliable and safe way, and will require significant work to do

Kent has admitted (many times) that snapshots are one of the more difficult features to add in a reliable and safe way, and will require significant work to do right, especially for what he wants to see them do (I assume "really damn fast and low overhead" is a major one, plus some other tricks he has up his sleeve.) So he has intentionally not tackled them yet, instead going after a slew of other features first. Reflink, full checksum, replication, caching, compression, native encryption, etc. All of that works today. Snapshots are a huge feature for sure, but it's not like bcachefs is completely incapable without them. There was a very recent update he gave in late December (2019) that mentioned he's actively chipping away at the roadblocks for snapshots.