Hopefully it will be added in one of the modes Pete Hines mentioned: https://twitter.com/DCDeacon/status/613517721989476352

For the people who want challenge, immersion, reactivity and fun - raiders can kill and raid your settlement.
For sissies... they can just disable that mode.

There - everyone is happy!

This is where the player's knowledge of strategy will come into play. Knowing that the wasteland is inherently hostile, a smart fellow will not spend the time and resources to build a settlement unless he can simultaneously put together a viable defense for its inhabitants. Like everything else that one does in the game- as in real life- you're governed by the principle of calculated risk. I agree that building a settlement and then losing it to raiders could be annoying. That's something to be avoided if at all possible. On the other hand, putting together a plan to retake it and succesfully implementing it can be quite satisfying.

seriously: i haven't seen one single npc in any beth rpg that could like climb or jump over walls.

i really think a couple barricades and a thoughtful choice of neighbourhood should do to keep your bunch safe

naaaaahhh... next step after retaking's cleaning up their booze bottles, dirty raider socks and gore collections, and scrub their friggin' genital doodle graffitis off the walls for days...

I really wish they'd let us build a catapult now. Throwing brahmin or dudes in power armor at an enemy would be hilarious!