Hi all, wanted to provide an update on this. To address some of the concerns expressed on this thread, we deeply value all of our customers, and we are excited to continue releasing features that make Coda more accessible and useful for everyone.
We’ve been working through the best way to integrate the unique first day of the week settings across our formulas and tables for some time now, and we plan to have a product update to allow this in January. As with many of our updates, we first need to complete the massive re-write of our core editor, which should expedite delivery on this feature and similar features to come. 
We appreciate all the feedback you all have shared!