As I currently understand it, the only way to access a shell is through the online shell. Being able to SSH in would be useful for:
1. Easy of use. I'm familiar with how my shell works, but in the online shell, it seems like some things don't work (eg navigating with the arrow keys or tab completion).
2. Debugging. I sometimes want to copy over a file (eg an output or log) to analyze locally, or upload some seed data.
3. Testing new code. One of our use cases is a dev server where we can experiment with code changes live (and on a machine that has all the dependencies installed, etc). We currently have an EC2 instance set up for this, and we'd love to replace it. With true ssh, you can properly edit things on a remote host.