Just swapped out my beloved 15" MBP 2017 for a M1 8/512. I'll probably keep the M1 for around five years. But since these are new times with the AS vs Intel, it may be that I'll upgrade sooner to douse my curiosity. However I'm quite certain that for my personal computing needs, the M1 will probably be good enough for a decade. 
My 15" Intel heater had loads of headroom left, and I originally intended to keep it until it was worn out, probably around seven years. But I will not be left behind on an old platform again, so I swapped it for this amazing M1 Air, that also fit my usage better these days, I really like the 13" size.
My 15" Intel heater had loads of headroom left, and I originally intended to keep it until it was worn out, probably around seven years. But I will not be left behind on an old platform again, so I swapped it for this amazing M1 Air, that also fit my usage better these days, I really like the 13" size.