Basically the ability for GM and players to lock doors, either via blockading it with objects, or having upon locking the door, a key spawn in their inventory.
Alongside this (and I would imagine that we might see this in the "Basic Building Destruction" that is listed on the Roadmap) is the ability to destroy doors, either with weapons or melee,.
Also, the same to be able to do it with Vehicles as well, with GM's being able to lock doors to prevent players for using them for whatever reason they feel necessary