"Bluntly, it would allow the creation of mostly “dumb” VR headsets. "
Changing the PHY layer would do ah heck-all to change this. The problem is that HMDs are inherently NOT dumb displays. This was tried during the early prototypes of the Rift, and again during early prototypes of the Vive. Both abandoned the 'it;s just a display!' approach as both learnt that it doesn't work in practice. You don;t get guaranteed refresh intervals, you don't get guaranteed refresh timings (critical for both synchronous and asynchronous timewarp), latency is all over the place, and it plays merry hell with trying to get applications to even display on the correct 'screen'. It is also completely independent of the PHY layer (occurs on both DVI/HDMI and Dispalyport) so changing that would improve nothing.
Whether Analogix can get this actually implemented is another matter. Spectra7 brought out a whole bunch of VR interconnect gubbins, but all that ended up being implemented was their cable tuning IC and Microchroma connector within the Rift CV1.