It's been out for weeks! I'm running it on my Mac Air as we speak...... I downloaded it from the Fortinet support portal.
The auto-installer installs an older version is the thing. I did ultimately find 5.4.2 after speaking with support, but it didn't fix my problem. For some reason now, whenever I enable either of my IPSEC profiles, I get an error -111. I've uninstalled, reinstalled, etc., but no go.