Epoch: The problem this is solving is M-of-N multi-key addresses. It lets you set up your wallet so that there are multiple keys, stored in different places - for example, one on your computer, one on your smartphone, and one in a safe - and require that several of them be used together in order to spend coins. That way, if your computer is compromised, the attacker can't steal your coins without also compromising one of the other keys. This feature is extremely important; it would have prevented the allinvain attack, it allows corporations to hold coins without having to completely trust any one employee, and it makes escrow work better. Implementation has to be done in two stages - first adding support for it in the protocol, then second adding support for it in the user interface. We're currently on the first part, and talking about the relative merits of different ways of doing it. All of the proposals currently on the table are protocol changes that enable M-of-N multi-key addresses, and pretty much everyone agrees that at least one of the proposals must be adopted.