If you have software development capability, you are absolutely correct that you can put together a new data attachment file and feed it back into the system. Devices can be configured to automatically pull updated data files. It is indeed a relatively straightforward task for any given individual form definition. What doesn't exist today is a general-purpose way to automatically set this up without software development. There is also no progressive sync capability so field workers would have to download the full updated data set every time it changes.
The threads at ODK ecosystem entity-based data collection table of contents are devoted to exploring formal additions to ODK to support these kinds of workflows without needing software development skills. We are approaching this cautiously because there is a lot of potential for complexity and some of the biggest strengths of ODK have historically been that it is relatively straightforward to get into and workflow-agnostic.