So you won't see us worrying about POSIX or the kernel VFS (virtual file system) interface.
...nor about compatibility between the on-disk file system format of WAFL and that of the BSD file system or the System V file system or NTFS or..., if that's what the concern about the file system being "neither BSD nor System V" was. (Then again, at that level, a UNIX machine using VxFS or JFS or XFS or... isn't "BSD or System V"; the file system's on-disk format is neither that of the BSD file system nor the SV file system, although it presumably provides semantics similar to one or the other or both.)
If the semantics of the file system, *as visible from clients*, don't match those that the client expects, that's a different matter; we intend to provide compatible semantics there to the maximum extent possible (the requirements of providing both NFS and CIFS access may constrain us here, and we might not be able to match the semantics of two different flavors of UNIX with different file systems without providing an option - for example, we have an option to control whether users are allowed to give their own files away, USG UNIX-style, or are not allowed to do so, Research UNIX-style).