If there would be an official guidance, then users could point developers to the guidance if they do not follow best practices. That would have some beneficial effect. In the past I have asked addon developers to apply some of the best practices listed above. But I am just an addon user with an opinion. It has much more weight if its an official practice that is expected of developers.
One thing that could be of use is to add a simple tickbox to the RM to select if the best practices guidelines have been followed. (with a link to the guidelines)
This way all addon developers are certainly aware of the best practices.