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" approa

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.