I think the term "Sandbox", and even "Open World" is missing the mark of what people really find interesting with games that they ascribe to that definition.
What UO had, and for some reason stopped pursing in earnest (Along with most of the genre it seems) is more properly coined
Emergent Gameplay. It's a method by which the developer creates a set of tools (The building blocks, if you will) by which the users of said tools can create their own content. There is also such a thing as unintentional emergence, where some things happen that were not intended (Second Life is a textbook example of this), but I think most of that happens because the implications and limitations of the systems are not properly thought out and implemented.
Somewhere down the line, it seemed UO just stopped looking at emergent systems. There are no more new or planned systems that are not just simply limited lifespan events or excuses to generate new items, or recreation of existing content. No, I don't want a UO like SL where people can literally write their own code and upload assets, but certainly there is room for more systems that allow for players to shape their own content and experiences with more consistent limitations that fit within the world.
***What follows is purely an example. It is not to say this should be done, but to demonstrate a methodology or thought process that is not being utilized to it's fullest capacity.***
Let's say we start with the new City Loyalty "system". It started out just doing three things - Putting out fires/cleaning up trash, capturing rioters, and giving stuff to angry citizens. Thankfully they started to add to this, and you can now turn in BoD's, resources, pets, even hunt monsters and get credit. And you can buy a title, or a nice banner. But where is this system ultimately going? I can probably tell you where it's NOT going, and why it's a missed opportunity.
So you now have a city loyalty you can declare for. The mistake was not making this loyalty account wide instead of character based, because think of what it COULD have been. Had they done that, your account can optionally be declared loyal to a city. Now let's take it the next step - What if you could opt into a PvP system that replaced factions and order/chaos, and was instead city based? And what if control of the city was actually done by players, determing what taxes to impose, levels of guard protection, alliances with other cities, what merchants to offer, elections? Now you have political aspects that players would play out in one way or another, even in no-combative ways.. But why do it for something other than pixel crack?
We have houses - Why can't groups of player houses create towns, with walls that can be built around them, and are associated with their closest city, and taxes are collected, and a new "capture" point is created for the opposing faction. If you take the town you collect the taxes. But what can people do to defend their city, their towns, from other factions? Siege to break down the walls and doors? Players being able to repair structures? What if a horde of zombies lead by Minax would attack the city with the most control points, taking those points until another city takes them back, making the city with the most control points make decisions about utilizing the content they've earned, and defending it from both players and NPC's? This sounds all well and good for a pollitcal or PvP base, but what about non-PvP'ers?
What if controlling the most control points opened a PvE dungeon? What if turning in resources to your city or making donations or the more towns your cities founded opened up other dungeons? Make new crafting recipes based on a city's virtue that you declared for, making a nice black market item to other cities. Make resources to make these items tied into to the PvE dungeons a city controls, giving a reason for people to partake in other play styles. Unique events that occur in them? What if you could set up a stall in your city, for a price, as well as have a housing merchant? And on, and on, and on.
Again, this was just an example system, not just singular events or occurrences, that lets players affect the world directly. It's a limited and shallow example of one, but even those aren't being considered. It's just release a dungeon, put new items with it, with no actual effect or desire to have an effect on the players.
Emergent systems are where the player is the dynamic, non-static focal point of any aspect of the game - not just incidental. And sadly, when people say they want a "sandbox" what I think they want is where their chosen method of play is relevant to the world, whether it's combat in PvP or PvE, roleplaying, crafting, or just exploring, and that they can CREATE a place for their role in the world, either among friends or everyone else. They aren't just things created BY a community - Quite the opposite, they actually CREATE the community around them. And in today's games, communities aren't really necessary.
UO started on that path - I wish they'd walk it again.
My opinion, of course.
