macOS has been using APFS
macOS Sierra had APFS since 10.12.0, but at beta capacity.
As other folks have pointed out, it cannot be used for startup volume like iOS 10.3 beta 1 can. And there are several other restrictions and compatibility issues.
Most significantly, Apple has been tinkering with APFS since 10.12.0. For instance, you cannot mount APFS volume from 10.12.0 or 10.12.1 with 10.12.2 and later.
And as of macOS 10.2.3, there's no way to do in-place conversion of HPFS to APFS.
iOS 10.3 beta 1 is using APFS for a startup volume AND is doing in-place conversion to APFS. So the only significant remaining issue for enabling APFS for macOS is (1) compatibility issue with some apps (case sensitive file system), (2) Time Machine support, (3) FileVault (should be mostly front-end and conversion work since APFS already has superior encryption), and (4) Fusion drive compatibility.