https://github.com/jupyter-incubator/enterprise_gateway to launch kernels on a cluster and https://github.com/jupyter-incubator/nb2kg to make a notebook server aware of them might be of interest (sans electron app shell).
I have lots of questions now, like why this isn't using the zeromq based protocol, so I guess I will need to spend some time with it.
It does look like it closely overlaps with what I was describing. I didn't realize overriding/extending the http api was even a thing that could be done so I just used zeromq for my own purposes :)