According to a press release from LG Displays, Apple will be following the Retina 5K Display iMac with the "iMac 8K." While the iMac 5K display features a 5120×2880 display, it is being reported that the iMac 8K will have a display somewhere around 16 times the number of pixels that a full-HD display has.
Apple has not disclosed any intention of revealing an 8K display iMac, but if they want to keep up with current competition they will. During CES 2015, LG revealed their own 8K displays with 7680×4320 displays.
LG's press release specifically names the iMac 8K, but whether or not this was a mistake or an accidental slip by LG has not been revealed. Here's a look at and excerpt of the press release:
It has become clear that Japan is planning to launch an 8K SHV test broadcast and then promptly restructure the UHD service. Apple has also announced that they will release the ‘iMac 8K’ with a super-high resolution display later this year. Korea is also preparing to offer an 8K service demonstration at the 2018 Pyeongchang Winter Olympics. LG Display displayed a new beacon of the 8K era by revealing their 98-inch 8K Color Prime Ultra HDTV at CES 2015.
Apple's current focus is on the release of the new Apple Watch, which has a surprising method of purchase — one that requires a little more work than buying a watch should require.