For the next generation hidden services project, we need the Tor network to produce a fresh random value every day in such a way that it cannot be predicted in advance or influenced by an attacker.
Currently we need this random value to make the HSDir hash ring unpredictable (#8244), which should resolve a wide class of hidden service DoS attacks and should make it harder for people to gauge the popularity and activity of target hidden services. Furthermore this random value can be used by other systems in need of fresh global randomness like Tor-related protocols (e.g. OnioNS) or even non-Tor-related (e.g. warrant canaries).
Proposal 225 specifies a commit-and-reveal protocol that can be run as an external script and have the results be fed to the directory authorities. However, directory authority operators feel unsafe running a third-party script that opens TCP ports and accepts connections from the Internet. Hence, this proposal aims to embed the commit-and-reveal idea in the Tor voting process which should make it smoother to deploy and maintain.