One thing I've found about k8s is running a cluster can be very costly, and using a managed cluster on one of the big three clouds is even more so. Also, when rolling your own cluster it requires a lot of elbow grease to get things in a working state, and even more to keep things working.
It feels awesome from a developer standpoint once you work out all the kinks. It's very natural describing your service with a bit of yaml, and then being able to then spawn it into your infrastructure and have it automatically scale out.
If there was a cost effective k8s cluster you could rent then that would be the thing that finally kills traditional infrastructure for me.