Making design fall under the community team umbrella (once it exists) makes a lot of sense to me, at least at the current size of the project. I imagine much of the material that designers would be working with/trying to make pretty would be generated by the community team!
Either way, I suppose I could just try pull-requesting the website and working on a style guide like a total autocrat and see who provides feedback and/or objects. 
I just joined/started #rust-design on IRC, which seems like the first step.