Keep the good work!
edit - some remarks to "get there": it must be/feel fast like native Excel, Sublime Text or at least VS code. In another phase, to be a real "programming editor" it would be great if you could use any programming language you want, not just JS. Clojurescript or Elm/Purescript could be a good start.
edit2 > ways to compress more functionality into the 'boilerplate' included with each sheet. I think the boilerplate should be somehow hidden from the end user.