We (https://www.ReactiveOps.com) run a lot of clusters for our clients in AWS (and also GKE, but..) using kops. It's definitely possible to run a lot of clusters, but kops is only one piece of the puzzle. Autoscaling, self-healing, monitoring and alerting, cluster logging, etc. is all other things you have to deal with, which are non-trivial (they scale workload per cluster, so...)
I saw you mentioned autoscaling first. How do you handle this? Do you just install autoscaler pod by hand? (edit: just saw the link you provided, not sure if you edited your post to add it or not, but thanks! I followed the link through to https://github.com/reactiveops/pentagon/blob/d983feeaa0a8907... and it looks like I would be interested in #120 and #126, but they don't seem to be GH issue numbers or Pull Requests. Where can I find more?)
It seems like a lot of the work like this just "isn't there yet" when it comes to orchestrators like Tectonic or Stackpoint, or Kops, in making this easy for you. (So there's surely a market for people who know how to do this stuff, but it seems like this would be the first feature that every tool supporting AWS would want to have. Unless there are hidden gotchas, and it seems like there would be a lot of blog posts about it if that were the case.)
We open sourced our kube generator code, called pentagon, which uses kops, terraform https://github.com/reactiveops/pentagon