Tim Berners-Lee has a long standing project that is part of Solid, and called the Data Browser (née Tabulator).
I think it is worth thinking about this as a model for a SAFE UI and even the SAFE OS concept.
If you sign up to try a Solid Pod, the current Data Browser is the UI you will see. Right now it is buggy and rough around the edges, but Inrupt are working to improve that, and there is a bigger discussion just starting on the Solid forum, where Tim just posted the following.
It gives insight into his vision for a Data Browser as a universal computer interface: