28"+ is awkward for 3840x2160. By rights it's mainly a niche option for videographers previewing video at that native size. Because:
- At 1x, everything looks super tiny. Menus etc. would be much smaller than on the 27" 2560x1440 units we're used to.
- At 2x (which Apple could easily add support for) everything would be super big! Not "retina" exactly--more like retina enlarged: you still see the pixels, and the fonts are too big!
But at around 24", 3840x2160 would make a great 2x retina display. THAT is what I expect Apple will do. Yes, it will have less equivalent workspace (and less physical area) than a 27" TB display, and so Apple will probably keep the non-retina TB display in the lineup too. But as a retina option, a 24" 3840x2160 screen would be great. Remember: retina MacBook pros have less equivalent workspace than the previous MB Pros. It's a compromise made necessary by reality. [
CORRECTION: greater workspace on MB Pros was optional.]
And that's just native res; at 2/3 scaling (like the retina MBPs offer) a 3840x2160 screen would offer a scaled (and still fairly sharp) equivalent to 2880x1620. Greater than the 27" displays' workspace, if you wish to use that mode and don't mind things being a little small. Again--exactly the compromise offered in the retina MacBook Pros.
Since 5120x2880 27"+ screens don't seem practical any time soon, I expect a 3840x2160 compromise from Apple for now. Sooner rather than later, please! Otherwise I may go Dell: portrait rotation is nice, but the speaker and camera situation is awkward at best, and Dell displays are super ugly. That matters: the monitor is the single biggest object in my living room/office! If the style of furniture matters to people... this thing is like furniture.
I'd love to have Apple's styling, speakers, and camera to go with my Pro.
(P.S. Don't forget that retina is defined in part by viewing distance: a much lower PPI than an iPad would still meet the goal since you sit farther away.)