I believe he stated in the beginning pretty clearly that the point of this exercise was to stress test the Liveview performance.

Making this more efficient would be kinda counter productive

I agree, but it certainly wasn't performant (in the video).

I'd be curious to see what parameters are required for a smooth / playable demo.

Or am I missing something?

(Slow input with no interpolation?)

I think the proposal here is to optimize for bandwidth by minimizing number of divs, because there are fewer divs per column per frame. It might actually turn out to be more work for the browser because it has to layout the columns with divs that are not uniformly sized.

That is!