Why do you need more than 2 Mpixel photos if you cannot say a difference without watching very close?
You don't, for a 66inch 4k tv an 8mp image will look better than a 4mp upsampled image at 2feet say or a 2mp image at 4 feet, or something like that. Now, we don't really need lots of res for screen or projection but for print, print eats dpi/ppi for breakfast and high-res images, well do the maths but a3/a2 images for print are hungry for your pixels, you should know this!
Lets dispel any absolute claims here. The first filter through which an experience happens is vision, each person's vision isn't necessarily the same. The term "spacial resolution" comes to mind here, it's really about at what point the pixels disappear and are no longer individually discernable. When that happens, it is technically, visually, no different than 4k or 8k or 50k. This will happen even with a 480p screen if you sit across a large room from it, the difference is that 480p screen will lose a ton of spacial resolution being so small from that distance.
So in essence, more pixels simply allows us to do either of two things: Increase the size of the screen without pushing the "event horizon" farther back, or, pulls the event horizon closer on the same size screen. So yes, there is a point (that which I refer to as the event horizon) which your eyes cannot resolve individual pixels anymore, at which point increasing the resolution (but not the size) will make no visual difference.
So the question is, for each individual person/display combo, where is the event horizon? If you are already beyond it on a 1080 screen, higher rez won't matter unless it also comes with a larger screen size which, from the same distance, will increase spacial resolution to the eye. For me, using my TV as a monitor, I sit pretty close usually. From 2-3' I could easily see pixilation on my 1080p screen. I cannot easily on 4k, even with a much larger display.
On some very thin lines I can see a slight jaggy when im about 2' away, so im right around the sweet spot of my viewing with this size (4k@49"). So the real point is, if you already can't see pixels on your lowly 1080p screen, going 4k won't make a difference unless you also plan to increase the screen size. Thing is with computer screens, people usually tend to sit pretty close to where 4k will improve the experience, and it's nice to be able to buy bigger without it just adding bigger jaggies.
Then there is more than just resolution to improve. For example the screen I bought is an IPS LED with 4:4:4 10bit color, and I have been going back through all my old photos and am just amazed at the quality. Color, sharpness, it's a huge difference. Video is also a huge improvement if it's 4k. Even if the EM5II did manage to match a 4k file on a 1080p screen, it will still get leveled when viewing on a 4k screen, and prices are dropping fast.
