I very much need this kind of functionality as well, in fact for several different use cases, for which I currently have to use another tool, but would love to move to Coda as soon as this functionality is available here!
Since you asked for more specific requirements, let me point you to a documented, powerful and most importantly sensibly general approach:
(watch 1:30 to 1:50)
In their terminology, @tomavatars Game “Title” and “People” would be categories (think dimensions); “Inside”, “Journey”, …, “Tom Avatars”, “Mat Lab”, … would be items of those categories; and the (existing and missing) rows in his example would - for the purpose of automatic creation - correspond to Quantrix cells. (His other columns “Link”, …, “State”, …, would be structured as items of further categories. And yes, both items and cells have something in common with Coda rows, because Coda of course does not yet understand the dimension distinction.)
While Tom only has two categories, the point here is that no matter how many categories there are (in any use case), when a new item is inserted into any category, several new new Quantrix cells (future Coda rows) automatically get created - one for each possible combination of items across all categories.
I’ve been using this sort of thing for many years, so feel free to ask anything further you might want to know …
PS: I think the functionality in question would really be a perfect fit for Coda, since it is a prime example of fundamentally rethinking documents (which is exactly what the folks of Lotus Improv and later Quantrix also did when they created what is essentially a multi-dimensional spreadsheet).