Tumblr has a plenty mature community — and one focused on very serious issues (Tumblr helped surface the Trayvon Martin story, for example). I know college professors who post there regularly. There are artists who do amazing things there (see:
http://annstreetstudio.com/). They would probably benefit from a customizable approach as well.
I think this is a mistake and you may find it hard to find users willing to submit content because you're not giving them much encouragement to post.
EDIT: Upon reflection, this statement was a bit harsh and I tempered it a bit, but I do hope you consider ways to focus on the user as much as the creator.
