I just took a quick look at the Getting Started documentation. The very first step for installing ShellHub how to, "... install and run a self-hosted instance of ShellHub on your local machine or on IaaS providers like AWS, Azure, Google Cloud or Digital Ocean." So you could go that way if you wished.
That would work in some circumstances. However, one challenge that most of us face is that the exposed IP address for our private network changes on a periodic basis. This solution solves that problem. Not to say it's a panacea, but it's something.
I suppose one could always explore renting a Linux server somewhere and run shellinabox on it. That might make for a good project some day if I ever find the free time. ;)
I just took a quick look at the Getting Started documentation. The very first step for installing ShellHub how to, "... install and run a self-hosted instance of ShellHub on your local machine or on IaaS providers like AWS, Azure, Google Cloud or Digital Ocean." So you could go that way if you wished.