I see these posts as a way for people to put up mini blog posts with a comprehensive write-up of specific topics or areas of concern. I'd love to be able to do this personally, since I feel I have the ability to contribute blog-quality content, but don't necessarily want to stand up my own blog to do it.
But there has to be some understanding about how these posts fit into the larger body of questions and answers on Stack Overflow, especially with respect to duplication.
A canonical post is supposed to replace any number of more localized posts. It is not a duplicate of those posts, and should not be closed as such. When someone asks the "headers already sent" php question, they post their specific code. The canonical post is supposed to replace those posts with a more general and comprehensive post.
There needs to be some sort of "post notice" letting the community know that this is a canonical post, and is intended to replace any number of "frequently asked questions" on the subject. The post (and its answers) can still be vetted in the usual way with votes, but there needs to be some leeway with respect to closing as a duplicate.
I'm on the fence with regards to CW. While I always CW and protect FAQ posts on Meta (which is our closest model to these canonical questions), if a person is going to put in the effort to write up a canonical post, they should be able to earn reputation for it.
On Meta, there is a special tag for canonical posts: [faq]. I would support a similar tag on Stack Overflow.