So the idea is this, if your colonist is unhappy, there's a chance that they will decide to leave with people from a friendly colony that is visiting. I guess at that point, you lose the colonist or arrest/attack visiting group, and become hostile.
Just seems like they come over so often, why would my colonists never want to see what life is like over there?
Agreed, and so would the opposite be viable as well, should your place be good enough. Way better than brainwashing hostiles into working for you.
There's a mod called Hospitality for recruiting visitors, but it hurt relations between you and the other colony. I've always wanted more diplomacy in the game, like someone from a friendly colony gets banished and they leave that person in your care. Rather it be the friendly colonies I could see neutral colonies doing this. Maybe an event could pop up where your colonist wants to join a visiting colony, you can let them, you get improved relations, and you get gifts every now and then from them, but if you decline they get stuck with a long mood debuff.
I'd like to see this happen with neutral-friendly factions, since there's little incentive to increase faction relations beyond not-hostile. I mean, sure, you could call for help, but they're generally too weak to make much of a difference and too slow to get to you if you really are in an emergency.
...That gave me an idea.