I think the dividing line really comes down to checking if something directly impacts community involvement. In the example about a blog, additional authors doesn't actively impact the community development. It does increase the number of people who might join the community by increasing readership, but they aren't a member of the community until they start commenting.

It would be an on-topic question to ask how to increase conversion of blog readers to comment contributors or asking other questions about increasing or improving usage of the comment system, but the blog posts itself are just a one way street.

That said, this particular case is also still a bit ambiguous since a more open blog can end up being a community itself since there are interactions between authors and we don't specifically mention that moderation has to be of an open community.

If the argument can be made that you are trying to form a broader community of authors, or particularly if trying to convert commenters into bloggers, then questions about recruiting authors would be back on topic since the goal is to form a community rather than just a couple of additional guest staff.

Perhaps the guiding line should be to ask "Is one of the primary roles of the position to interact with the community?" If so, then they are functioning in a community development capacity.

In the example about a blog, if an additional author primarily develop's one way content and doesn't actively interact with the community any more than an author or news reporter would, then they are not acting in a community development capacity. They may increase the number of people who might join the community by increasing readership, but those users aren't a member of the community until they start commenting. If, on the other hand, the blog authors were also expected to interact with readers in comments, then their selection would be on-topic since they also have primary responsibility to interact with users.

It would be an on-topic question to ask how to increase conversion of blog readers to comment contributors or asking other questions about increasing or improving usage of the comment system, but the blog posts itself are just a one way street.

That said, this particular case is also still a bit ambiguous since a more open blog can end up being a community itself since there are interactions between authors and we don't specifically mention that moderation has to be of an open community.

If the argument can be made that you are trying to form a broader community of authors, or particularly if trying to convert commenters into bloggers, then questions about recruiting authors would be back on topic since the goal is to form a community rather than just a couple of additional guest staff.