If I may extend your metaphor, the problem then becomes the scaffolding that lies between architecture and features. Another attempt at a rule of thumb is to as

If I may extend your metaphor, the problem then becomes the scaffolding that lies between architecture and features. Another attempt at a rule of thumb is to ask the question: can I describe how this likely-but-not-yet-needed change would be addressed in the code? If there's no answer (or the answer is not satisfactory), the question becomes: what do I need to do to have a good answer to the previous question? And so on.