I think there's always an element of that possibility as there's always something better on the horizon. Certainly been enough threads asking whether to wait for the next gen CPU/GPU.
What makes the Zen 2 CPUs like Threadripper and Ryzen 3000 series more exciting is the actual architectural changes. And we can certainly see the benefits of going from Zen + to Zen 2 from the benchmarks. Whereas Intel's consumer CPUs haven't really seen much innovation since Sandy Bridge. This will change when Intel finally have a new architecture like AMD has in recent years. Not sure how far the scheduling issues have been resolved with Threadripper, with respect to Windows anyway, but definitely a force to be reckoned with.
Then there are the cases where you have no choice to upgrade because of failing parts but can't wait until the next new release.