4K (4096×2160) and Ultra HD (3840×2160) are different things.
From what I read media believes Ultra HD is 3840×2160, but is sometimes called 4K because 3840 is near 4000, when it comes about television. So, in the media's view, there's no proper 4K resolution for television.
While they're at it, they might as well add support for 8K too.
Maybe that's what exactly what they have done. Check it out one more time:
Originally Posted by Phoronix
The X.Org Server DDC code now needs to read the max TMDS frequency field in the HDMI CEA vendor data block to check the mode dot clock.
I'm not really familiar with this "CEA vendor data block" (I think it's part of the CEA-861 series, this one dealing with transmitting more data than vanilla EDID using extensions to EDID), so I don't know if it has support for 8K. But if it does, the wording here gives me the impression that 8K should then also end up being supported.