But what would the specific implications of that be? I mean, would MS Office work in 5 years on it? What would I specifically lose the ability to do?
As someone who has owned (and still owns) a lot of older Apple hardware and used it long past its expected lifespan, here’s what it’s like:
At first, your older machine works just like a newer one would except slower: you can run the latest OS and most of the latest apps without even thinking about it (in the PPC-to-Intel days, Intel-only apps started popping up within a year or two though). Then, you stop getting updates to the latest macOS, which is still fine because most software keeps support for old versions for a couple release cycles.
Eventually, though, you start running into issues where new apps or updates to existing apps no longer support your OS, so you have to go out of your way to find old installers or alternatives that still support your system. For stuff like Office and most creative apps that’s fine: you can be as productive in Office 2008 or Photoshop CS2 today as you could when they were released, as long as you don’t mind missing out on new features (I often prefer old Office and iWork releases myself). The real kicker is when Safari stops getting updates, and then Firefox, and eventually Chrome. At that point, you’re at the mercy of fellow old hardware enthusiasts to compile modified legacy versions of those browsers just so you can use the modern web.
I used a PowerBook G4 as a secondary computer (my main portable) for a while between 2014 and 2016. It did almost everything I needed it to despite it being on a dead architecture (for macOS, anyway) and 10-12 years old, but there were a lot of tweaks and research and hoops to jump through to get it to play remotely nice with the rest of the modern world. I also regularly used a laptop stuck on 10.11 up until November of last year when I got my 14” MBP, and went through a lot of similar headaches near the end. The point of buying an M1 Mac over an Intel one now is that you won’t hit that tipping point of “still relatively usable, but increasingly unsupported” as soon.