My vote is for stabilizing existing features, especially when it comes to issues affecting the usability of already supported devices (example).
Minor wishes:
The webui could use a little polish when it comes to UX and taking advantage of modern screen sizes (small and large). Some documentation could be embedded into the webui as an installable package.
More responsive OpenWRT wiki and website, more documentation in the wiki. The experimental new TOH is a massive improvement from the old one.
Dev blog (What is being worked on? What are some interesting obstacles developers ran into?)