I think (as I said in the previous discussion) that the key issue with the lengthening phone upgrade cycle is security patches.
Manufacturers are trying very hard to have built-in obsolescence: https://www.theregister.co.uk/2018/05/31/dutch_court_says_sa...
Unless this fundamentally changes, most non-techy users will have to needlessly upgrade perfectly good devices, run insecure software or become much more savvy about which manufacturers are better in this regard - and the outcome is likely to be some malware has a very large distribution followed by a lot of press.