Maybe @wendell can get some more info.
Pixio's Roadmap on Facebook
In the comments, Pixio mentions that they are "preparing" a FreeSync 2 display. Also, a revamped PX277. I for one cannot wait seeing that GSYNC HDR monitors will be no less than $1000, a clear money grab. And I have no doubt even at that price they will sell out.
Also, it doesn't seem like there is support for Dolby Vision on either GSYNC HDR or FreeSync 2.