I’m with you, the community management aspects of the UI could do with some love.
My quick thoughts:
Sorting by the columns in the list of communities page
Have the search field not jump to the generic search, but instead apply a filter to the table (which can then also be sorted by the columns)
In the Subscribed communities sidebar, also have a search field that alters the list of communities to only those that match the search
In the same sidebar, allow users to place communities into folders or lists that can be folded or expanded so that users can easily navigate to user defined subsets of their communities. Currently it’s a flat list alphabetically sorted.
Either in the side bar or the communities list page, list the number of posts in that community today. I don’t know how viable this is, but each community’s sidebar shows usage data, including the number of users/day, so something like this must be possible.
Much more ambitiously, and it’s already in the GitHub issues but I’m mentioning it here anyway, 4 above naturally leads to providing a feed for only a selected user defined folder/group/subset of groups, so that they’re not merely for organisational purposes but like multi-reddits a nice way of customising your feed.