The Apple File System is designed to scale from an Apple Watch to a Mac Pro. APFS is optimized for Flash/SSD storage, and engineered with encryption as a primary feature. The new file system is available to developers in preview form right now and is expected to be launched in 2017. The pre-release APFS can not be used to boot a device and, for now, does not support many Mac staples, including Fusion Drives and Time Machine. It is uncertain the data you put on a drive today will be readable by later versions of APFS.
Source: https://thehackernews.com/2016/06/apple-encryption-file-system.html