I bet somebody could make a business refurbishing those old 5K iMacs into usable monitors. Either yank the panel into a new case w/ a custom board to drive the display, or hack an input into the existing system (maybe with a minimal booting OS).
Either way, that'd be a cool product to see and seems like a decent side hustle to get some $. :)
I recently bought a 2015 27” 5K (5120x2880) iMac core i5 for cheap, put in an SSD, and upped the RAM to 24 GB. It handles everything I can throw at it as a developer (albeit not a game developer, just “full stack” web/java/node/k8s) and the screen is just incredible.
The SSD upgrade is not for the faint hearted, however. I used the iFixit kit with the provided “tools”, and lifting off 27” of extremely expensive and heavy glass that sounded like it might crack at any moment was not exactly fun. Having said that - I would do it again in a heartbeat to get another computer/display like this for the price I paid.
With regards to scaling: I have had zero problems with either my rMBP (since 2013) or this iMac, when in macOS running at high resolution. Zero. As soon as I boot Windows or Linux, however, it’s basically unusable unless I turn the resolution down.
Either way, that'd be a cool product to see and seems like a decent side hustle to get some $. :)