When I visit the root domain I shouldn't be greeted with a marketing splash page, you need interesting content in the user's face right away, entice their curiosity and drive the user to explore the site... even as a fellow developer, my first instinct is to abandon the page as soon as I'm greeted with the cliche startup marketing page. Consider the user experience when I visit reddit.com or news.ycombinator.com or any other link aggregation competitor. What you have now is a tech demo, not a platform. Sorry if that's a little harsh, but I mean well! Good luck!
On the contributor side:
- Visual style guides require much more time and skill to create (relative to style guides for code) and still generally fail to achieve anywhere near the aesthetic unity of a single great designer with total control.
- If you commoditize your design elements to the point where it is easy to contribute them, then it is no more difficult to do it yourself to begin with.
- Delegation of design work still requires that you funnel it somewhere to be judged on qualitative measures, rather than the pass/fail nature of code
Generally the best you can do is collaborate very, very tightly and then funnel it through a single person in the end anyway a la Python's BDFL in a very trial and error fashion.