(Why save a few dollars when you can get extra capacity instead? Especially when you have $100k of someone else's money to burn... so, for real though, anyone who has actually tried this configuration can chime in and confirm that it works as well as I imagine.)
I'm pretty sure that periodically shutting down some nodes is a boon for cluster utilization, too. One of the things that Kubernetes does not do on its own, is load rebalancing. You can configure the autoscaler to recognize when nodes are overprovisioned, and let it drain a few and shut them down... or you can let the preemptible nature of (some/all of your) nodes do it for you.
(Why not both? Some nodes are getting killed, or you're paying for resources you don't use, so... one way or another.)
I got introduced to the Kubernetes ecosystem when Deis Workflow was rebuilt for it. Today, I'm a core contributor on the team that is building the fork of that project.
(It is a side thing for me. I'm very interested but I'm not spending hundreds on infrastructure every month. I have an infrastructure team at $dayJob, and they are not doing K8S at all, if you are having a hard time understanding how exactly I got here.)