I'm thinking about the implementation of pseudonymous reputational systems. I think this is a key element, which is missed yet for a development of an agora. In fact, we have Tor hidden services, we have bitcoins and Open Transactions for creating a banking system, but the open problem is about the reputation of a bank if it is a Tor hidden service.
The concept for reputation I prefer is the one suggested in http://ilja-schmelzer.de/network. But it needs to be implemented. So I would like to find people interested in such things.