The Stack Exchange framework in general is designed for expert questions and answers. That doesn't necessarily mean that on any given Q&A site in the network novice questions aren't welcome. On some sites related to academic work graduate level questions and higher are the minimum. Sites like StackOverflow tend to welcome questions from beginners and provide at least hints towards students doing homework. The key is that someone answering is an expert. Expert won't necessarily mean a Caldecott winner answering on children's books or anything. Expert Alan Kay answered a question or two on StackOverflow and that didn't change the course of the site. The highest reputation point holder over there, though, is a fairly noted expert in one of the main programming languages discussed on the site.
So while we don't need to narrow our focus only to writers who have writing as their day job (and shouldn't), we do need to attract sufficiently knowledgable people to the site. They should feel that answering questions is worthwhile and even that they might get questions of their own answered at the expert level. I think also that we want others in the industry of writing and publishing on the site, which means that some level of focus on professionals might naturally develop.
We should welcome people who want to write because they love to write, whether or not anything they write is ever seen in a wider audience. I'm not sure what our focus audience has to do with eschewing convention specifically. Perhaps you can clarify there.