Thanks. I've created an issue to add mathics support (via the Jupyter kernel) to SageMathCloud: https://github.com/sagemathinc/smc/issues/417
It's awesome that there's a free open source Mathematica-like program now.
I'm working on a fully featured jupyter kernel that will eventually get merged into the main Mathics repo [1]. I was planning to inquire about some hosting in a couple of weeks (once my exams are over and I have a chance to finish the jupyter kernel off).