My concern is that every time a new version releases, vital documents are not up to date. That confuses new developer and set back on pushing upgrades. I wish I have an architecture document and learn this entire framework through the document. Thus, I could be more confident about any changes in the patterns and develop with confidence.
I believe many developers just want to implement their plugins quickly to satisfy their requirements. In order to do that, they need fundamental knowledge of the nop design patterns for 'previous' & 'new' nop versions. Any competent developer can do this but it takes time, as the only method right now is to review existing code bases from freely available plugins.
Maybe if nop offers project templates/extensions in Visual Studio (VS) to quickly generate project plugin libraries, like in VS. Have project templates for plugins such as payment, shipping, discounts etc and include basic design pattern sample code for the developer to fill in to follow best practices (eg. how events are implemented in nop for specific scenarios). Sure, this is somewhat spoon feeding but the software vendors goal is to implement and get the job done for a return of investment of their time.
It may help and draw in more plugin developers.