Heh, I was looking through some of the old videos and articles on the 2014 Mac mini, and basically everyone complained about it at launch, mainly because it lost RAM upgradability and because it's slower than the 2012. However, I'm coming at it from a different perspective since I just need it for business applications, and in 2022 I don't want to be stuck with Catalina for official support. I've come to really like Big Sur's new look, and I also like some of the small little new features in Monterey. Thus, after initially considering the 2012, I eventually decided I wasn't interested in the 2012 at all, despite its ease of upgradability.
Even if Monterey turns out to be the last macOS for the 2014 Mac mini, I or a family member can continue to happily use it until 2025 at least. Getting macOS 13 like
@NewUsername suggests would be really nice though. I guess what s/he suggests is that would be like the upgrade from Sierra to High Sierra. All the machines that got Sierra also got High Sierra.
I do have to agree about that entry level 4 GB i5-4260U though. That machine was unimpressive even in 2014. The upgrade to the i5-4278U is quite a big jump. Sure the price difference back in 2014 was significant, but it came with much higher CPU performance and also doubled RAM and storage. And in 2021 the price premium for this configuration on the used market is only ~$50 or so.
As mentioned, I've been using my 2017 Core m3 MacBook to power my 30" ACD, and its performance is nearly identical to the i5-4278U (according to Geekbench measures) (although the Core m3 gets more advanced video decode acceleration). Overall, I've been quite pleased with the CPU performance of the Core m3 for my applications, so I'm sure I'll be pleased with the CPU performance of the i5-4278U too.
The 2014 Mac mini is a bit of an edge case because it lasted so long. Bear in mind that at this stage it can have Monterrey whereas the 2013 MacBook pro (and 2014 model) both have Haswell CPU as well but because they were discontinued within a year of introduction they don't qualify for Monterrey - the 2013 MacBook Pro tops out with Big Sur.
My feeling on the Apple policy on OS support is that they'll offer
at least 5 years - plus 2 years of security updates to match the next two OS versions.
It's the hardware repair that is listed as up between 5 and 7 years after a product is discontinued. This becomes harder when a vendor (such as Intel) discontinues parts such as CPUs. In this case I think Apple would offer a refurbished more modern equivalent.
Sometimes Apple need to discontinue because Intel are scrapping the CPUs they are relying on - the Coffee Lake CPUs going into the current 2018 Mac minis were relatively quickly discontinued and in part forced the hand of Apple who have to stop production of the mini soon because Intel will have shipped their last pile of CPUs.
The mobile CPUs that went into the older minis were much more longer lived - partly the reason why the 2014 model lived on so long despite being long in the tooth.
The 2014 model went off sale in October 2018, I expect it will get a new OS until October 2023 - 2 versions after Monterey - followed by 2 years of security updates. You're in luck.
Whereas people with older MacBook Pros 2013/14 don't officially get such support despite having the same hardware.
It's easy to get sanguine about that but it's a long period of support for sure. Owners of the 2018 mini are also in luck - because the so-called 2020 Mini (where it received a spec bump) is not an official model - it's just a spec bump. So 2018 model users still have a 'current' Mini which will receive updates for 5 years after it's replaced.
Currently, this should be 2026/27 (plus 2 years of security updates) by my reckoning even if the Intel minis get discontinued in favour of an ARM Mini - sometime between now and WWDC 2022 I would have thought.
By the same token then 2019 Mac Pro can expect to get the same length support - perhaps even longer if they don't replace it till October 2022 by the time next year's OS comes out.
Remember also that the 2013 Mac Pro - the trash can - only went away in December 2019, people who bought one in 2013/14 could easily expect support until September 2024 with updates for 2 years after that - a long time indeed.
Apple can still make certain newer features ARM only (or mandate T2 CPUs as they are a natural limit) - and it's easy to say that the iMac didn't get T2 until very recently (2019?) whereas T2 MacBook Pros have been around since 2017.
At the end of the day, if you need an Intel workflow you're best getting a currently on sale Intel Mac now rather than trying to save a few quid by looking for a used one. iMac 2020 is still on sale whereas the Intel iMac Pro was discontinued in August 2020 - short of the introduction of Big Sur.
That means the iMac Pro might not qualify for whatever OS is released in October 2025 but probably will get security updates until September 2027.
Whatever happens Apple will want rid of older edge case Macs as soon as practical, and while T2 is a natural borderline Apple need to wait till
October 2026 (well over 5 years after the iMac 2019 27" was discontinued in August 2020, but the iMac 21.5" 2019 stayed on until April 2021) and then every Intel Mac prior to that will have had at least 5 years support by Apple standards. So owners of T2 Macs older than that might get more support than they bargained for if Apple are treating T2 as a borderline.
In terms of edge cases, the trashcan Mac Pro 2013 will be end of the line by this point, the long lived 2014 Mini will also be done for (if not sooner), The 2016 MacBook Pros with the T1 chip will have had a really long support period if they last this long too so they probably shouldn't get too discouraged if they've lasted till 2026 but I equally wouldn't be surprised if Apple let them go by 2025.