It looks like from here on out Protogon is no more. WinUnleaked has found that latest builds have removed Protogon support and replaced it with a new file system. Be prepared to hear "ReFS" a lot from now on, as this new system is better supported than Protogon ever was. For a start, the disk formatting utility actually lists it as an option.
At the moment, Windows 8's installer doesn't play nice with ReFS. Users are told that the system can only be installed on NTFS-formatted drives. It's entirely possible that installation isn't supported because the feature is incomplete though, so at this stage it's hard to say how finished versions of Windows 8 will treat ReFS drives.