They way I read it is that the new TVs will need to support HDMI 2.1, which has not been ratified yet. For now, you will need a PC monitor that supports Freesync over HDMI (remember that freesync was originally a DisplayPort standard). This is how I interpret the information out there currently.
I´m not sure, how Xbox One X will support it, but based in pc to TV 4k , using HDMI 1.4 with any cable, you can reach 4k 30Hrz, in 2.0 with 18 Gbps cable you can use 4k 60 hrz on 4096x2160 res, with 27.7Gbps cable you can use 4k 120Hrz.
In theory Xbox will support HDMI 2.0 TV´s using freesync or not
Edit: On Xbox system you can set the resolution that you want and lock or unlock the framerate, so i dont see a issue.
And the important part:
There are now tens of HDMI & DisplayPort FreeSync monitors on the market. Bad news is HDMI doesn’t “officially” support the Adaptive Sync feature that FreeSync relies on to actually work. DisplayPort 1.2a and newer iterations on the other hand do. The current FreeSync via HDMI option is thus an ad-hoc solution, one that AMD has made a lot of effort to deliver to the market. This is why we haven’t seen nearly as many HDMI FreeSync monitors as we have seen with DisplayPort.
Bringing Adaptive Sync over to HDMI and thus to the masses of console gamers and home theater PC owners is an absolute necessity at this point. And perhaps the most important industry wide move forward in gaming and display technology in decades. It’s then clear that AMD’s efforts to bring FreeSync to HDMI were well calculated and far-sighted. Why exactly we haven’t seen HDMI pickup Adaptive Sync to date and make it officially part of the spec is a head-scratcher.
Although have no doubt, it’s simply going to be a matter of time before every console gamer and HTPC owner can enjoy this incredible technology on their TV from the comfort of their couch. 4K is exciting yes, but If we end up with a stuttering juddering mess that we can’t possibly enjoy then why bother at all. If you have ever had the opportunity to game on a variable refresh rate monitor then you know exactly how big of a deal it is. If you haven’t then I urge you to try it, it’s truly eye opening.
Since FreeSync via HDMI is an AMD creation because the blockheads at the HDMI consortium are probably living in the age of CRT and slide rules and need to be slapped into 2017, the answer is that nobody knows for sure. Heck, nobody even knows what the GPU will be inside of the XBONEX and PS4P, be it Vega or a refined Polaris, just that it's a semi custom 14nm APU from AMD of the power of the RX 580.
So the answer is: Wait until it releases and the reviews confirm what works and what doesn't, because Microsoft and Sony aren't talking.
I guess FreeSync over HDMI will be with hmdi 2.0 as its new, I think now all new monitors will come with hdmi2.0 as a standard. But you can check on that list from AMD,you can see all the monitor able to deliver it, you will certainly to have to download the manual of each of these to get your answer.
Freesync 2 and hdmi 2.1 are backward compatible, only handshake wise, meaning if the limitations of your monitor is FreeSync 1 and HDMI 2.0, then the xbox one X will deliver these capabilities to your monitor, but not FS2 and HDMI2.1.
But for now, none of these, FreeSync 1&2, work. Why? I dunno. But it will definitely be available in a near future. So any monitor on the amd list with FreeSync over HDMI will work, when xbox one x FreeSync option will be ready.