No snapshotting yet, can't boot, no migration tools for existing setups (time machine, filevault, fusion). It'd be interesting to see whether their permission changes introduced in 10.11 will travel further down the fs. Also, I don't see any mention of compression like lz4. Lots of work until release in 2017!
On the other hand, people (sample size: my family and friends) tend to fill up their drives with already-compressed video and photos, which lz4 and similar cannot really compress further.
Because you can upsell a larger iCloud subscription to your customers using the new built in automatic cloud archival function.
Then use compression server-side. $$$
lz4 really helps with anything that is compressible - if you store text or compressible data it can improve throughput up to 2-3x if not even more if it's not compressible it stops compressing early. On a modern CPU core compression/decompression throughput is in the range of multiple gigabytes/seconds.
