I like this idea and I can think of a few sort of lovely sagas which I'm going to list but not sure the best way to link them.

Couples: Kate Warner and Bill Pardy, Kaylee and Simon, Gordon and Alyx.

Plots and trickier things: The Ford sisters, Susannah Dean and her family, The Nobodies though they did a lot, but my favorites are the stuff with Rachel Grey, Coyote, Marvel Civil War again this plot covers a lot of people and I was involved with part of it but I love all the different ways, Milliways brought it to life.

I know there's more but this is just what first comes to mind for me.