depends on the socket. AM4 is planned to be around till 2020, while intel has already abandoned the previous boards that share the socket with coffee lake. forced upgrades are as intel as x86. intel makes the chips and the chipsets and profit demands that each new chip and chipset are mayflies. use em while you can because the upgrade window is limited.
will 9th gen chips force a new motherboard?
Historically AMD supports sockets longer than intel.