I ponder what they would even need to upgrade to go from X470 to X570. It sounds like the only real difference is probably just taking advantage of PCIE4 by slapping more or better stuff on the board... that won't realistically effect a vast majority of people.
Otherwise it seems that efficiency gains will reasonably offset other aspects as to make most upgrades moot. Maybe an upgrade for the low-end to more reliably handle the new CPUs? Maybe the top-end motherboards will get Overkill-VRM to prepare for seriously overclocking the rumoured Ryzen9 part?