Yeah, I think adding NPC guards to your claim would be a nice feature. They'd protect your shit while you're not around,ifyou opt into PvP. If some dick decided to trash your shit, they'd have to deal with the guards you've stationed on your claim.
Now suppose you and your guild have all joined your claims and built a massive city with walls and guards. A rival guild decides to declare war. When they attack they'll be fighting your guards and trying to get through your defenses, but what if the game also decides to let you know your house is being attacked? You might get an email/text saying, "Your guild fortress is under attack by enemy forces". Now you and your friends log in and start fighting the invading guild. It turns the end-game of Landmark into a castle raid/defense metagame, at least for people who opt into PvP.
This is exactly the kind of shit I want to see in Landmark.