To your points: - yep. It is unfortunate. Always stick to the default folder structure (subfolders for modules) to prevent any weird interactions among engines

To your points: - yep. It is unfortunate. Always stick to the default folder structure (subfolders for modules) to prevent any weird interactions among engines and between engines and the main app. - Prevent this by not allowing this. You would not have different dependencies within one Rails app and you can't have it with a component-based architecture. - Routing between engines should be much less frequent than routing within. A perfect case for preventing unnecessary dependencies by creating "engine routing intrefaces"