An opposing viewpoint: please don't add any of these suggested features. I prefer the programs that manipulate CSV to only express the actual contents of the file. Formulas are the antithesis of that. The beauty, and utility, of CSV is its simplicity. All of the requested functionality can be easily performed in SQL, Excel, Pandas, R, Krangl, etc. Please keep formulas out of a CSV editor.
I agree with that purity argument, but I wonder if it really has to preclude all spreadsheet calculator ambitions: just take the "multiple files project" approach and make it good. One csv for raw data, one csv for configuration/formulas, one csv for intermediates/results.
Make full use of whatever awesome multifile read/edit the software presumably has already and then maybe go a little beyond. The "configuration" csv might have some hashbang equivalent defining a line offset for the header that isn't mapped into input/output files (perhaps a concept of "negative line numbers" for project properties?), contains references to those peer files and maybe activates project options like "display peer file contents in cells that are otherwise empty" if you want your working surface to remain "2d".
The argument to have this add-on (I'm not sure that it should be part of the product or a separate extension) would be that it would be a shame to learn all the UI ergonomics of the plain reader/editor and then not be able to leverage them for some calculations as well.
I am not talking about per cell formulas like in Excel. I am talking about a basic expression language that operates on the entire column, more like a database. Modern CSV already has some basic data transformation facilities, I'm only suggesting a few more in the same vein that make it a more potent data editing tool.
Possibly the most efficient and effective method here would be to integrate Lua into the internal data structure used for cells, and let replwoacause do whatever they like with a scripting language. I can definitely see how that would be useful to people.
I would actually be wary of trying to make this too much like a spreadsheet, even in appearance. You'll be pulled into that strange attractor, but you can't hope to compete in that space. Whatever oxygen isn't consumed by Excel itself is long gone between LibreOffice and online spreadsheets.
