Much Like the Title says I think having a roaming band of Gypsies roll up to your settlement (once it reaches a certain stage(s)) and set up a temporary camp outside of your settlement. You can investigate, nothing much maybe trade some goods or what not. At the second night the Gypsies camp will come under attack (Insert whatever is lvl appropriate based off of your settlement rank) you as a settlement will have 2 choices defend the Band or let them fend for themselves. Defend them, the Band leader will approach your settlement banner and wait till you click on it
(roll in a cut scene - pending how intricate Radiant/Modder wants it - A few of your settlers around the camp fire with the Gypsy Band leader.
From there they will spin a Tale of some sort leading somewhere to start a quest(s)
If you leave them to fend for themselves the survivors will curse your settlement (maybe get a few extra raids the next night or something).
If you complete the quest(s) they will be friendly to the settlement and every so often (when your settlement rank increases) return with a new long lost forgotten tale to spin and send you on another quest(s).
Just a Idea for a few quest set up scenario’s.