If any of you are familiar with Karina Longworth's podcast You Must Remember This, the Manson season from a couple of years back was excellent. The concept of the podcast is that it can spend an episode exploring all the interesting things that intersect with a small part of the larger topic of the season. So it had a whole episode just about the film history of the western movie set that later became the Family's home. There's also one episode about his friendship with The Beach Boys' Dennis Wilson and their long attempt to get Manson a record deal (it involved ordering his young female followers to do sexual favors for LA's music industry people). One thing that I always found bafflingly underplayed in pop culture and history's assessment of Charles Manson is how utterly fucking racist he is--people glum on the crazy hippie cult leader thing, glossing over the fact that his main objective for his cult was that they would bring back black slavery.
I assume any of these aspects would be entry points for Tarantino. Which is why I'm really hoping it's not just about the Tate murders, which is usually the only aspect dramatizations and fictionalizations of Manson ever really mine from.