I think that's rather ambitious due to the file sizes. Plus most phones barely due 4k still.

It’s at least a nice option—I don’t own a single device that can play 4k video (and have it look any better than 1440p), but at least it’s available for people who have new televisions. YouTube downscales automatically for logical bandwidth usage.

Monitors too. There's a rise in 2k but still very few 4k monitors out there. Also even if phone's did 4k, is it really work on a 6" screen?

4k monitors have been $350 or less since 2015. I know because I got one then. There's far more 4k screens than 1440p (wrongly called 2k by some people).