Not sure why anyone would be bucking for Hyperion itself to effectively throw away what is pretty much their meal ticket in favor of a UI replacement that no one is really asking for. Why would they? Progress? Why change what works, especially when users can customize the UI themselves anyways *if* they choose to. I'm a big fan of the bare bones, no bells and whistles Hyperion bone stock WB.
That, in some sense - is like wondering why Ford doesn't simply throw away the design paperwork for the Mustang because some guy is shouting that the Pinto is a more apt choice for what is their most recognizable/flagship auto, lol.
If another UI experience is something you'd like, assuming you're even an OS4 user - there's options like DirOpus, many choices for themes, and if you're so inclined, program your own solution for it. Voila.
As for Ambient and MOS, it's an acquired taste. I am a registered MOS user, and I like the OS very much, but I'd be lying if I tried to tell you that I care for the design of it in the least, so I mostly use OS4. That's a matter of personal preference only - many people are the exact opposite.
Were the default OS4 experience to suddenly be retooled to look like an Ambient knockoff, I'd quit using OS4.