Btrfs has had LZO and Zlib transparent compression support for a while now -- we've been benchmarking Btrfs compression going back six years. However, patches that have come about for Snappy compression as well as LZ4 compression never end up being mainlined.
Published today were the latest patches for Btrfs LZ4 support by an independent contributor, "Like lzo in btrfs, this patch added lz4 compression support so that
users can have a third option."
The response to this new patch was this Btrfs FAQ entry: "Will btrfs support LZ4? Maybe, if there is a clear benefit compared to existing compression support. Technically there are no obstacles, but supporing a new algorithm has impact on the the userpace tools or bootloader that has to be justified. There's a project idea Compression enhancements that targets more than just adding LZ4. Reasons against adding simple LZ4 support are stated here and here. Similar holds for snappy compression algorithm, but it performs worse than LZ4 and is not considered anymore."
Expressed is that Btrfs with LZO will not provide any speed-ups or space savings, disk format changes (such as by adding a new compression algorithm) are permanent, and it needs to fit in well for how file-system I/O works.