I'm using a 43" 4K TV as a monitor now, and I really like it. It does take some getting use to at first, but with a tiling window manager I can split it up how I like and have the benefit of being able to use the whole screen at once for games and movies. Higher pixel density would be nice, because I still need subpixel text rendering to make the text look nice. But with 8K TVs coming out and getting cheaper, that would make a good combination of workspace size and decent enough pixel density.