Hmm how about a UI-prototyping community?
Steemit.com's UI person is https://steemit.com/@pkattera I think. Other than that there's the @sndbox guys who's doing that @creativecrypto magazine-layout website. Yeah just out of my head atm. Oh and also there's where you can list and find out the apps around Steem (not sure if they're actively updating it) https://steemprojects.com/
Just followed @pkattera, but his last post was 5 months ago and last comment 7 months ago, so I'm not sure how active he is anymore with UI work here. I'm finding add-on's that help a bit with the UI and finding content, but since quality has both intrinsic and extrinsic properties, it would be best to have a UI and economic reward system that recognizes that. By intrinsic properties I mean properties of the content itself, such as whether it is original vs. copied, accurately achieves a stated goal, etc. By extrinsic I mean factors like the size of andinterest/needs of an audience, as well as other things going on in the world. For example, I find the Mathematica StackExchange site to have very high quality content both intrinsically (because there are so many detailed answers theres) and extrinsically (because I use Mathematica every day and often need to get help on StackExchange). On Steemit, I think higher quality content could be found much easier if the UI supported communities that could both curate and better organize content around some theme. This would address the extrinsic aspects of quality (that of audience interests). Some of this is being done organically here, but the UI doesn't really support the efforts, so it is done through browser add-ons, curation accounts, and other apps. That makes things really messy, especially for new users who are likely already overwhelmed by everything Steemit. The strange thing is that the models to do this area already out there on Facebook, where they are clearly successful and of value to users.