as of 2017-02-02
Apple is selling the LG UltraFine 27″ display for $974 until March 31st, according to current announcements. After that, the price is scheduled to return to its original list of $1299.
But Apple is currently selling a second 5K display for $1799. Its just called the iMac 27″, base level version. This means, comparing “list” prices, the Intel Core i5, and its four USB 3.0 ports, the ethernet port and the two Thunderbolt 2 ports, and the 1 TB 7200 rpm hard internal hard drive are worth about $529 – effectively a 4-core Mac mini. And it includes its own keyboard and mouse. So you do get quite a bit compared to the Mac mini.
Or it would be a second display except for the fine print: Apple Support document HT204592 includes this little zinger: “iMac (Retina 5K, 27-inch, Late 2014) and later iMac models can’t be used as Target Display Mode displays.”. The document was last changed 2017-01-11.
I believe this is because Thunderbolt 2 does not support 5K data streams.
So to use an iMac this way, it needs to be a non-5K iMac, preferably with Thunderbolt support: iMac (Mid 2011-Mid 2014). That makes those used machines perhaps a lot more attractive as a second machine than the current Mac mini. They should make an interesting Time Machine device. Although, a primary iMac cannot send data directly to any of the Target Display Mode (“TDM”) iMac’s ports, the TDM Mac remains running, and TDM can be turned on and off using Command-F2. Those iMacs have Thunderbolt 2, so if your Mac has Thunderbolt 3, you need the “Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter” to make the connection. All of the iMac Retinas produced to date do have Thunderbolt (1 or 2) ports, and so can be the primary machine to a TDM iMac.
I expect to revisit this topic after the iMac 27″ Thunderbolt 3 (Early 2017) is released. If the lowest priced iMac 27″ remains at the $1799 price point, and supports Target Display Mode, then there would be no pricing room for Apple to sell a separate 5K, standalone display.. And little reason to use any engineering resources to design and produce one.
Apple could produce a port-limited iMac Retina with Thunderbolt 3 and sell that as a 5K Apple Display. That would have relatively little additional engineering costs and almost no difference in production costs. But unless the lowest priced iMac Retina Thunderbolt 3 costs much more than $1799, there still wouldn’t be a price point to sell it at.