Really I thought 2.1 was hardware based ?
HDMI 2.1 will have a controller that's certified to do all the features.
But the old ones can still be reprogrammed to have the features added in at a later date.
The new LG oleds that just came out released with HDMI 2.1 and the 2080ti has already been patched to include the new HDMI 2.1 vrr feature and also can run the screen at 4k 120hz.
https://www.google.com/amp/s/www.po...019/9/10/20859422/nvidia-g-sync-lg-oled-4k-tv
This is news article from last year with them talking about it and it was added in a driver update a couple of months back.
As long as the hardware that was originally added was powerful enough for the new features they can just be added in at a later date.