Traitors

[SirLeonardo]

Visitors could go to your colony in a reasonabel number an well-armed,and when they enter your hall,they attack your colonists or when the colonists are sleeping they attack and pirates could go to your colony telling they are from other faction(the colonists can't know from which faction they came)and attack at the same condition i telled before.

[Kelvas]

Ooh, this could be particularly "FUN" for villages you've done something negative to.

Example: Group of visitors is hanging out around your base, and you're tired of seeing their ugly butts/want their stuff. You shoot the majority of them and chase them off. Thinking them sufficiently disinterested, you go back to your regularly scheduled programming. Your attack was egregious, but not enough to flip their faction instantly to hostile. Next season, they send another group of visitor traders, except much better armed. They post up in the middle of your base and then... Ambush! They switch to attacking! You should have known better to let in a faction that you've slighted!

I like it!

[SirLeonardo]

And with this,visitors or traders could be entirely exterminated and with no hostile faction,they tell "ok,no problem",and the next time they visit you they bring a little army,kill half of your colonists and burn all your colony.

[Luroshard]

Visitors could go to your colony in a reasonabel number an well-armed,and when they enter your hall,they attack your colonists.

or focus on kidnapping someone
the whole idea of traitors sounds !FUN! when you put it together in a big prison break.

[firescythe]

I would bond succesful traiters to good infiltration skill. Otherwise they should behave "strange". It is a nice idea to make someone get into the colony by masking intention, however without any slight heads-up I would totally anger up. Killing off recovering patients, doing close combat hit on sleeping colonists... It has happened to me that with melee skill13 my guy hunted a deer. On first round the deer poked out one of his eye. Can't imagine what trouble an infiltrator assassin would do. In a low population survivor camp, where there is only 1 doc, a good grower, maybe a good shooter... some of them gets permanently wounded or killed by a welcomed stranger... So I would make it conditional to population, faction relation, wealth ratio, etc.

[Limdood]

no thank you.  "gotcha!" is never fun.

[keylocke]

stealth, betrayal, deception, mystery, etc.. hasn't really been tackled that much in rimworld.

the way the "story" is being played is so "in yo face" and straightforward that it leaves very little to the imagination.

meanwhile, there is a game out there called the sunless sea my delicious friends.

if you want to see a good sample of how mysteries (or the lack thereof) have a huge impact on storytelling, then the sunless sea may provide a good stage to see how something similar can be applied to rimworld.

as for the OP's suggestion.. this somehow reminds me of the red wedding. 

maybe someday those factions you've betrayed before can attend one of your parties and/or weddings and then do just that.. haha..

now that is a dynamic story you'd never see in most RTS games.. 

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edit :

iirc, in the old alphas there was actually an event that randomly turns one of your colonists into a traitor, but it was poorly implemented back then.. (it was mostly just pure random between berserk, daze, betrayal, etc..)

probably coz the old alphas didn't have the same relationship systems that we have now.

in a13, people actually remembers how they are being slighted. colonists hold grudges and keep friends and lovers.. there are social fights that occasionally leads to murder.

so betrayals and stuff like that ought to be reevaluated eventually in the future.