What I think is missing is a way to help the author (and other team members) make sense of the artifact as it gets more complex.
Much of the development in computer languages and toolsets in the last 50 years have helped us make sense of ever-increasingly complex programs.
With spreadsheets for example, you are basically forced to find a cell that seems to have data you like. Then you have to back-track formula references + check for macros/scripts and hope that no references have broken.
I humbly submit this is a problem that a team like the Coda team should be solving.