I often reflect upon how my life has a really badly written narrative arc! (This is also, I think, the challenge of writing fiction based on real people - it's more satisfying with a narrative arc, but how much is it ok to change without being misleading about the subject/main character?)

I feel like comics with big sprawling canons is probably where I've seen interlocking/overlapping stories and side stories most often. I guess you could probably do it with anthology TV...and romance writers do like to introduce main characters of future books as side characters, but I feel like that's a bit different somehow. Hmm. Not sure. But neatly focused narrative arcs are the easiest to approach, I guess.