Their ZFS encryption is vulnerable to watermarking attacks, so most people don't want to see it publicly used anyway.
While a bit cumbersome and arguably suboptimal, at least on FreeBSD you can use geli+zfs to get full disk encryption.
Sure, but that doesn't help in the context of zfs send, which serializes at the filesystem level for transport. The stream is still going to be in plain text. In fact, Oracle's ZFS still sends the stream decrypted and decompressed, even if those properties are enabled.