Before Clone Wars became cancelled and ended with season 6, George Lucas and Dave Filoni were thinking of adding an arc that explained the entire story of the Sith Temple underneath the Jedi Temple. I think this would have been interesting to learn more about, and would help us to understand why the dark side clouded so much of everything, as Yoda said, and how Palpatine hid his true self right under the noses of the Jedi Temple.