Storytime is a hard presentation style to get right. It's really good when done well, because people like stories. It's a difficult presentation style to get right because it's very easy to get lost in a story, or overload the story with too many details that aren't relevant to a larger audience, or forget to be very clear what the moral of the story is. Your session description is a really good one, which bodes very well for getting this style of presentation right.

For the user experience of your audience, it should be transparent to them about how you choose which person is speaking. I don't think a ball will work because it will make your audience focus on the ball itself ("when will it be the other person's turn?") instead of what you're actually saying. You don't want them focusing on the mechanics of your talk, you want them to hear your content.

You could structure a deck around the morals of your stories, and determine in advance what stories you're going to tell and how you're going to make them compelling stories to people who don't know anything about Dreamwidth or its history or its politics or its userbase. I think that the challenge that you are going to face is that you have a lot of stories to tell. Figuring out which are the best stories to tell to this audience such that they'll get something out of it that they can take back to their own projects is going to be difficult because you have so much material to choose from. And you want a really strong finish to wrap up your session, it's what people remember, so figure that one out in advance.