Since Apple abandoned subpixel antialiasing with Mojave, I’d be running Windows 10 and/or Linux on the machine as the full-time OS.
You're abandoning macOS because of subpixel antialiasing, but you want to use a monitor that's been running for 7 years, is out of warranty, and can't be repaired by Apple? None of that makes sense. Just reenable font smoothing from the command line. Or go ahead and run Windows or Linux, with their thousands of apps that don't support font smoothing, despite the OS supporting it.
Most important thing to me is screen quality and nothing on the market under 27” competes with even these old iMacs.
This is just not true. You could be correct if you qualify this with, "Nothing competes with even these old iMacs
for less than X amount of money. But many, many high quality, 1080p IPS displays exist for <$200 today, some with actual 10-bit color support, unlike the iMac. You could also use a Spyder for further color calibration, if you need it. And do you really think a 7-year-old screen is going to have uniform brightness?
For this to make sense, I’d need the iMac to last at least 5 years. What are the chances a 2014 refurb makes it to 2026? And what would be the first thing to go? I’d be booting from an external SSD, so that’s not a problem.
There's no reason to think the iMac is
likely to fail in the next 5 years. But there's also no reason to think that
any computer or monitor is likely to fail in the next five years. If you're playing the law of averages, any single device you pick up will last that long or longer. But you're guaranteeing yourself no warranty repair--and no out of warranty repair!--if you buy the iMac. I don't know why you'd want that risk.
My previous LCD monitor went bad after roughly 10 years. That’s probably my biggest concern.
If you think you should be able to count on an LCD lasting for more than ten years, you should be concerned. You say you are really concerned with "screen quality" (however you define that), you should also recognize that, just like CPUs, SSDs, and any other tech you can think of, LCD/LED/OLED screen quality improves year after year. That doesn't mean every monitor is good, just as not every 4K TV panel is good. But monitors today are better than in 2014, and monitors in 2028 will be better than ones today.
If your question was, "How can I buy a Mac with the best possible screen for <$500 Canadian?" I'd agree with your answer. iMac screens are better than MacBook Pro screens, and you're not going to get an iMac for <$500 if it's much newer than 2014. But you can just buy an old Lenovo ThinkCentre for $200 with an excellent IPS screen for $250 if you just want to surf the web with the finest display you can buy (under $500).
