Emacs already has that, included in org-mode: https://orgmode.org/org.html#Tables
(Emacs also has an even more spreadsheet-like mode; ses-mode, but that saves its data in less-than-purely-textual format. Or, at least, less textual than org-mode.)
If you could invent a text format that could be efficiently edited with a basic text editor then I would agree it's a DSL. But I feel like you would lose a lot by dropping a dedicated GUI, e.g.:
- horizontal scrolling of columns, adding, hiding columns
- "smart copying" a formula by scrolling down
- selection of rows/columns/cells
I don't think anybody would use such DSL using a basic editor.
Overall it's discussion about the definitions of terms, but I don't understand why people want to capture anything having some "editable format" as a "DSL" when addtional terms like "visual programming" allow more differentiation?
That's an unjustified qualification. I could throw together a spreadsheet format that is all text. The spreadsheet GUI then becomes a advanced text editor that, when editing that particular format, exposes advanced content-aware controls not at all unlike advanced text editors like emacs can for s-expressions.
We can bridge the gap in other ways too, for instance the '2d' racket language that lets you do control flow using a two-dimensional ascii art grid: https://docs.racket-lang.org/2d/index.html It's not hard to see how this concept could be iterated on to become something quite like a spreadsheet, and with editor support the editor/language combination would begin to look a lot like a spreadsheet too.