I am a big fan of K8S too, not only use it in production, but I was also the one that set it up for my team. I agree that, unless you are already familiar with it, it is not always useful for protyping stage.
There is something to be said about having the infrastructure in mind though. That's why I'm inclined to use something like Elixir/Phoenix for web-based projects. Some (not all) of the ideas that K8S brings to the table are already built into the Erlang/OTP platform.
As for Heroku, there was a recent announcement that I think shifts things quite a bit: https://blog.heroku.com/buildpacks-go-cloud-native ... having standardized container images that runs buildpacks.
The ecosystem and tooling is not quite there yet, but I can see this as significantly reducing the investment to put into Dockerizing your app for K8S.
At that point, for the hobbyist, it might be:
Prototype -> Heroku -> K8S with an Operator that can run the buildpack
K8S is really a toolset for building your own PAAS. If there were a self-driving PAAS (using Operators) targeting small hobbyists that will run cloud native buildpacks, then the barriers of entry for a hobbyist using K8S is much lower.