Unless I'm misreading, the page seems to indicate that only external volumes can be formatted with APFS. My guess is that they'll have limitations and HFS-defaults for several years, at least on macOS, as the file system matures.

Either way, what file system didn't take years to get right? There are so many possible edge cases with file systems that it not only takes a long time to sort them out, but an amazing community and/or luck to reproduce deterministically to fix them.