But I don't get why it's a tease since it's an episode that takes place when the concert isn't happening in a place that's just in the general area and ends with Roger saying good-bye to his daughter he barely spent time with outside of that episode, so why would her being there draw him to Woodstock? He can get stoned and laid in his hotel room.
Wasn't that part of the point, that the house had nothing to do with Don? Megan chose the place where she wanted to live and there was no place for Don there. I feel like Don might have even had a line to that effect (beach vs. canyons), but I can't remember where or when or what it was so I might be making it up. But still, I think they can put Megan the actress in the canyons and intentionally bring to mind the future Manson murders without having Megan actually run into any of them as part of a story or having Megan's reactions be a focus.
Right, Megan's only in the one episode months post-murders and she's getting officially divorced in it. In fact, with these locations specifically it seems more like the point was the opposite. The fact that a NYC-based cult group might naturally settle in the Woodstock area is a handy way to invoke Woodstock to underline the generational conflict in that episode that ends with Roger flailing around in the mud. Likewise Megan moving to a house in a canyon is a better symbolic fit with what the move means for their marriage. It's specifically not Don's idyllic California beach. In fact, it's the part associated with brutal endings.
But why change the whole timeline structure that ends with the moon landing just to have a reference to Woodstock because the audience knows about it? A lot of the obvious themes to use these events for were already used in earlier episodes like Mystery Date, Tea Leaves and The Monolith.