I see thanks AntiBlitz!
It reminds me of some mods in Minecraft where you could "claim" blocks with points, and then except your allies noone could modify them, not even open doors.
It created anti-grief kingdoms where most of the threats were internal, like recruiting a troll who then stole and threw explosives everywhere.
Then you could declare war (tresspass, fight claims) to other kingdoms but it was a transparent act and you were warned and could then react appropriately.
If it stays as you said I think there shouldnt be too much problems.
Even though I dont share your optimism on "digging for hours/days just to shit other people? Na. People arent that dumb", yes they are
I think that there will be at least local events where bandits use every unclaimed or fought over lands as very interesting grief place.
I can already see people digging extremely complex secret tunnels to access to some shit or possibly collapse buildings, if there is physics in this game. But then it will still require extremely large amount of time and effort just to do something that you can do with extreme ease in other games, and its good that they already planned anti-grief system to counter the worst.