Congratulations, this is awesome. One of those "why hasn't someone done this already?" projects.

I can see this becoming transformative and superseding Excel, which is a bold claim to make. But this is compliant (with Excel), performant, extensible, free, and in-browser. This could easily become almost an emacs-level editor.

Think of the interfaces that could be built to this in this?

I'll be sharing this with every student I know.

And the name is a winner.