Well, this is interesting and I get what what people are saying, and I don't know where in the world everyone lives, but they are broadcasting 8k in Japan and some cell phones have 4k displays. Having said that, we need to know what you want 8k 120Hz for.
2D or 3D? in 2D, it takes less GPU power so in theory, 8k @ 120Hz might be done in 2D but not 3D.
While it is somewhat different technology.... there is a processor inside that tv driving 8k pixel density...... and it isn't some over priced $2000 Nvidia GPU. It is probably some cheap ARM processor or what ever they are putting in TV's now. So just to dump an 8k feed to a screen at 120Hz should not be hard.