I still can't believe Apple that makes a 27" iMac with a 5k screen can't repackage that screen as a stand alone product.
...because the end result would probably have almost no components in common with the iMac apart from that l-shaped stand.
Internally, the iMac drives the display via a custom interface that can handle 5k@60Hz.
The only
external interface that can handle 5k@60Hz in a single stream is DisplayPort 1.3 which is still as common as hens' teeth and, crucially,
not supported by Thunderbolt 3 (or the TB3 incarnation of USB-C DP alt mode) or Intel's integrated GPUs. All current
external 5k displays use
two DisplayPort 1.2 connections, each driving half of the display.
Thunderbolt 3 is capable of combining two "virtual" DP1.2 connections into one TB3 cable - but inside a TB3 display, that is split up again into two DisplayPort signals.
So the internal "architecture" of an iMac and a TB3 display are very different. Externally, the iMac case is unnecessarily big for a display, too (the old TB/Cinema displays
never used the same case as an iMac, even before the iMac was slimmed down).
Essentially, the LG Ultrafine 5k
is what we'd have got if Apple had made their own display, just without the pretty aluminium-and-black-glass box. Oh, yeah, and these days 'natural' anodised aluminium isn't good enough for Apple, so they'd have to make separate "silver" and "space grey" models too...
Actually, I can kinda understand Apple getting out of the display business until Thunderbolt 4 comes along and, hopefully, brings some sort of single-stream 5k display solution.