It's all the bloody same and they all know it. It's just software locks on Nvidia's side in software/firmware/driver.
This new firmware is being used now for future Native G-sync screens, and the Acer Predator XB273 X is the first we’ve seen advertised with these new features. We confirmed with NVIDIA that it will NOT be possible to update firmware to any existing Native G-sync screen, or request updates to allow your current G-sync screen to be updated so that it would work with AMD graphics cards. The new firmware will only be applied to future G-sync module displays.
Yeah they are not too keen on updating anything on those modules, ever. What you buy is what you get, no updates at a later time by anyone, certainly not by customer.
If they want to keep selling those modules, they have no other choice but to support HDMI Async and allow any source to work in Async mode. The sales amount difference between Gsync moduled monitors and Async capability provided by the many other probably finally dawned on them.
No one sane will purposefully choose a Gsync moduled monitor at a higher price if an alternative exists and it's often significantly cheaper or even offers better specs and runs cooler.