Hmmmmmm it's a fascinating one this.
1. I got 8 years of use from a end of 2009 white MacBook BUT it was so underspeced that at 3 years old along with the Mavericks OS, it was a pretty horrible experience - super slow, spinning beachballs on Safari etc.
2. I had a 2015 which was replaced with the new 2017 due to battery problems.
3. For me, the new MacBook 12" is wonderful (My FAVOURITE Apple design) BUT i'm not convinced that it will last more than 3 or 4 years. It's so lightweight and fragile.
4. What i've learnt is BUY APPLE CARE and maybe DON'T SPEND MORE THAN YOU HAVE TO.
5. Therefore, you are covered for 3 years and after that, who knows.
6. Maybe just buy the M3 in its basic form and enjoy and then trade it at 4 years. That's what i'm planning. I'm just gutted that I need 512GB as £1550 was a heck of a lot of money for something that may not last long.
MAIN MAJOR ADVICE - BUY APPLE CARE = 3 to 4 years of pure enjoyment. Any extra is a bonus plus in 4 years time, the MacBooks may of evolved into something that you'd be desperate to get your hands on

Who knows Micro LED? Apple's chips instead of Intel? 24-48 hours battery life???
But it's the same with an iPhone £800 or £1000 and after 3 years, it's pretty useless in speed, battery etc etc. I've the iPhone X now on a 2 year contract, so i'll do like I always used to do and upgrade my phone every 2 years. My old 4S, I kept for 5 years - loved the design BUT after 2.5 years the OS updates slowed it down so much that it was nasty to use and after 3 years the battery would last 3-4 hours or if I used Google maps, i'd get 5 minutes before the battery died completely.