I don' get the dead platform thing unless you are someone who has to have the newest CPU every gen. A lot of people looking to upgrade seem to be coming from CPU's 3+ years old and if you keep the new CPU for a similar time by the time you may want to upgrade again, there would have been enough advances in tech that it will warrant a motherboard upgrade anyway.
This. How many people actually upgrade their CPU while the same socket is alive? I never have that's for sure. Even on AM4, I fully expect that processors released in 2019 will require an AM4+ board with a newer chipset. Technology moves forwards all over the motherboards, not just the CPU.