Screen Real Estate is King
but I'm not quite convinced that 28" QuadHD is a sweet spot for a computer monitor. The pixels are going to be uncomfortably small at 1x, and at 2x there's not enough screen real estate for my liking. If there was a 1.5x mode in OSX (or arbitrary scaling), then I'd be a lot more happy.
This.
For me also (and I'm sure I'm not the only one) it is about preserving (or increasing) usable screen real estate (seeing more on the screen without scrolling). My ACD 30" shows 2560 x 1600 and these 4K monitors are 3800 x 2160. So at 2x (retina) I lose 660 "pixels" worth of width and 520 "pixels" worth of height. That's a big step backward.
And if I run it as 1x (native) I think it would be too small to read. So it would need to be 5120 x 3200 to maintain everything I already have and add retina. What is that - "5K"?
I do have a 1680 x 1050 version of the 15" MBP however and the smaller pixel size on that is acceptable, so I could take some reduction on pixel size compared to the 30" and still be happy. Maybe a 36" monitor running 4K would be usable at 1x.
I know that the Retina 15" MBP can scale at two intermediate resolutions (1680x1050 and 1920x1200), so if that same ability gets carried over to external displays there may be promise for preserving screen real estate until even higher resolutions of 5K+ become available to allow true retina for 30"
I also want to keep the 16:10 aspect ratio. I do work on this thing - it is not my home theatre screen. And if I do watch a movie, some letterboxing is fine.