After a second viewing, I'm picking up more computer MMO RPG game references. The original movie was based on Disney-style theme parks, but this new version is more based on computer games. The Hosts then are NPC characters that are supposed to follow a set script. The first time I watched, my expectations from the original movie led me to think that maybe Ed Harris was a robot that escaped 30 years ago and found a way to pass as human. But now I'm taking his "game" references at face value.
Looks like there's a river boundary that separates the "safe zone" in town from the wilderness outside. They mentioned that there's more "adult" content not suitable for children on the other side of the river. I assume some kind of non-deadly "Player vs Player" combat can take place there. The Man in Black/Gunslinger is bored of just killing off NPC hosts, so now he might be trying to find a way to "hack" or exploit the game to become a "Player Killer" for real. Getting away with murder, without attracting the attention of the team running the game.
I was actually IN the Ultima Online beta back in 1997, when THIS happened:
http://griefing101.blogspot.com/2010/01/defining-moment-assassination-of-lord.html