Events and bosses will still spawn mobs, but you have the power to control time now.So will turning off all spawns even work during Blood moons and Eclipses? Because having some way to just totally ignore those when you don't feel like dealing with them, particularly Eclipses, has been a long time Terraria wish. It's annoying when you're focused on building and then an Eclipse says "Nope, time for monsters everywhere! Now you can't focus on building and simply being within spawn range of your NPCs endangers them." Temporarily turning off spawns entirely seems like it should be a pretty good workaround as long as the spawn control setting always has priority.
Alternately, a way to make it so that areas with enough NPCs to stop standard monster spawning can stop Eclipse and Blood Moon spawns as well would be cool too, for non-Journey solutions to that annoyance.
I can definitely see mods popping up that disable godmode or allow you to change difficulty settings before entering the world and be unable to change them in the world, as well as a mod to restrict what can and can not be duplicated.It might be complicated but I'm sure the modding community could create extra features or costs for the Journey character/world type. I'm not too sure how this works in multiplayer, but being able to keep everyone on the same limitations would be nice too.