Dell UltraSharp 32 Ultra HD 8K Display Suggests that an iMac 8K is Technically Feasible
See my Mac wish list.
See also Too-High Pixel Density on 5K and 8K Displays Impedes Image Assessment.
Update 10 June 2017: the Dell UltraSharp 32 8K Monitor UP3218K is shipping.
While I saw firsthand the LG 5K display for the 2016 MacBook Pro, unfortunately I did not chance upon the Dell 8K 32-inch display which was announced at CES.
7680 X 4320 pixels = 33.2 megapixes in 32" form factor, aspect ratio 1.77:1
A 4K display is like tiling together four HD displays and thus requires 4X the bandwidth of a conventional 1920 X 1080 display. An 8K display is like tiling together four 4K displays for a whopping 33.2 megapixels (7680 X 4320).
A a full resolution Nikon D810 image is 7360 X 4912, so its entire width fits with room to spare on an 8K display, although the aspect ratio is too tall to fit vertically. The pixel density of an 8K display has to be an awesome viewing experience, but high pixel density is problematic for assessing image sharpnesss.
The $4,999 UP3218K is slated to go on sale on March 23rd. It has a refresh rate of 60 Hz and will work with zero Macs and only a few select PCs with specialized video hardware, and even then GPU performance will need some time to catch up. The display supports 100 percent Adobe RGB, sRGB, and Rec709 color gamuts.
HDMI 2.1 (announced at CES) supports 8K, but Apple doesn’t even support HDMI 1.3 yet, so external 8K displays are likely to take a few years to become more than a special rarity.
However, at least in bandwith terms, 8K might already be possible; see: Can a 2016 MacBook Pro support an 8K display?
Potential for an iMac 8K
Since a 32-inch panel now exists, it seems ideal for an iMac 8K which could use a custom graphics solution to push those 33 megapixels—no need for wait for standards to evolve to support external 8K support; it can be done internally just as with the iMac 5K.
The Dell display will apparently sell for $4999. Even assuming that Apple could use its considerable volume to get that price down to $2000 or so, it would make an iMac 5K with the necessary GPU power something hitting the $6K to $8K range in price. So even though it appears to be ideal for an iMac design, pricing is an obstacle that could put off an iMac 8K for a year or more.