Btw Arstechnica nerds are debating this a lot more than we are here right now. The side that says "Well 1080 monitors can never see a difference, its placebo or youtube sucks" are putting up good points, and the other side "Well its not just youtube, its everything that looks better in 4k on my monitor" are also putting up good points. I think the former probably makes more sense, but with my own eyes and current technology im seeing the latter. So im just just not care that much for a few more years until it actually matters.
But I think objectively, there's no reason not to get a 4k monitor right now if you have the money. Why not? It clearly can be different.