I think we could make the loading state really cool. Ideally the whole table would show some sort of loading state, so even if you are scrolled past the header, or if the header is hidden you can easily see it. We could show a marching animation on the entire border of the table or something.

We could also better show this in the code editor when the cell runs. The code editor border could also have the same loading animation, which would visually tie it to the sheet the code editor while loading a nice way.