The architecture of the SoS kernel, if we ignore the SoS workflow engine part, is just a Python3 kernel that sits between Jupyter and all other kernels. The SoS kernel starts the subkernels, collect user inputs (interpolate them if needed), send them to the subkernels, and collect and display outputs from the subkernels. Data exchange between subkernels are implemented by executing hidden statements in SoS and subkernels, with assistance from SoS language modules for supported languages. This simple setup introduces minimal changes to Jupyter users: they can use multiple languages in a SoS notebook but can also use the SoS kernel as a wrapper to their kernel for an improved frontend, and they can enjoy all the tools that Jupyter provides (e.g. JupyterHub, template, conversion tools) with SoS Notebook.
Finally, the name SoS Notebook comes from the fact that it is a frontend to the SoS (Script of Scripts) workflow engine. We know it does not sound great and places SoS well behind the real "SOS" in a google search, but let us just hope that some day SoS would appear in the first page when you search for SoS. :-)