User Directories in Diaspora
One thing that I really like about RedMatrix is the concept of the directory. In a nutshell, it provides an opt-in federated directory for members on hubs to make use of. This can be useful for several things:
Contact discovery - many people moving to the federated web have difficulty finding their friends, who could be on any pod anywhere. A directory could make finding friends much easier, regardless of where they are.
Censorship resistance - rather than being a centralized directory, members that opt in are mirrored between directory server sites, and any of these mirrors can provide directory services to smaller sites or those that don’t wish to take on the directory role themselves. A tally is maintained for how many times they've been blocked by people in the network, but it's up to the podmin to decide whether to block it in their directory or not.
Currently, Diaspora makes use of content discovery through profile hashtags, but it's not federated across all instances in the same way.
Just some food for thought.