Thoughts on related issues -- over & above style guide recommendations ......
John,
Core pages: These are pages that are not in the main or user namespace, and at the moment, I can't really think of any instance in which they require more, less or different guidelines.
Sponsored pages and otherwise: I'm not sure this is the way I would want to classify the different sorts of projects going on. If you look at the "Style and content types" conversation on this page, you'll see that I'm thinking of classifications more along the lines of "solo", "private collaboration", and "open collaboration". Private collaboration would be the sorts of things you describe as "sponsored", and then I break down the rest even more into work the author doesn't want any help with, and work the author(s) want everyone's help with.
Now, solo work, and I really don't think I'll change my mind on this, belongs in a subpage of the author's user page. The namespace already holds the meaning that nobody should touch it but the guy whose name is on it. Why not use the assumption as an advantage, instead of other tedious methods of designating the work as solo? The work can still be categorised, and there are lots of tools to deal with the cumbersome titles.
It was that idea that led me to think that we can use other namespaces for the very same advantage. The main namespace already very clearly and traditionally says, "everyone's", so that fulfills the needs of that sort of classification. But, we don't have an "ours" namespace, so I think we should make one. I'm not coming up with any good names for it... any ideas?
