I downloaded Catan onto my Xbox 360 a couple days ago, a virtual version of the board game.
I love it. In fact, I think I've become a little obsessed with it. I'm sure that's partly because the A.I. players have been wiping the floor with me. On Hard and Medium difficulty against 3 players, I think I've won maybe 3 or 4 games out of dozens. It's as much luck as skill, so I don't feel too bad about it... but I confess that sometimes I get that old feeling from my childhood that the A.I. is somehow "cheating" or conspiring against me. It's possible the game is designed to tip the "luck" portion into the A.I.'s favor when you get close to winning (I'm usually ahead before I lose), but for now I'm chalking that feeling up to paranoia.
Anyway. I've been wondering whether features of Catan could be adapted to MMORPGs, and I have a few ideas. Basically, this is how one might complicate Realm-vs-Realm gameplay through a combination of goals and boons.
Players join NPCs factions (ala SWG) to compete over regional control of resources. For example, one mountainous area might be a source for ore. Your faction must gain control of that whole area before you can harvest ore from those mines (possibly just one mine).
Two ore regions might be next to each other, or they might be on opposite sides of the map. Some lands might have some resources but not others (like Freeport missing wool, while Qeynos misses ore), so invading enemy territory is sometimes necessary to supply yourself and sometimes mainly to cut off your enemy's supplies.
There are more than just 2 or 3 realms, and realms can form trade alliances. That, and a small NPC supply of every resource in each region (subject to inflation when not supplies are not matched by player harvests), ensure that no faction is every completely bereft of any resource.
The design would be complicated, but it it might be possible to tie alliances with momentary needs. Rather than faction A and faction B always being allied in trade of everything, each realm's needs will change month to month. One month, you need wool and lumber, so you trade with factions B and C. The next month, you have a surplus of wool and need ore, so you shift your trade alliances to those who have ore or need wool.
It would be best if these changes in need were not totally artificial, if they were tied somehow to viewable dynamics or changes in realm actions and strategies. In Catan, you need bricks and lumber to build a road, but you need grain and ore to build a city. You will need to build both roads and cities, but odds are you can only do one at a time. Your needs change as your focus changes; sometimes in progression of your overall strategy and sometimes in response to your opponent's actions. A similar system would be possible in an MMO.
In Catan, you can spend resources to buy a card. The card will be chosen at random from five possibilities, some more common than others. The cards are Soldier, Bounty, Monopoly, Road Buider, and Victory Point. It's probably possible to work all of them into an MMO, but it probably makes more sense to mimick only a couple.
The Soldier card
This one's the most common in Catan, and it serves two functions: (1) it prevents surrounding villages or cities from producing resources; (2) it seizes one resource card from an opponent.
In an MMO, a realm could spend resources to hire NPC guards for a resource area, limited to some number.
Realms might also have opportunities to steal resources from other realms (as opposed to conquering and capturing an opponent's territory). Each player bears the mark of his or her realm, so everyone's aware of which faction you belong to. Every player may reference some part of his user interface to be reminded of where realm alliances currently stand. Afterall, your realm might shift trade alliances while you're offline. To guard a resource area though, you need only keep an eye out for anyone not of your realm, because even allied realms cannot generally be allowed to harvest from your area (you never know when your ally might get greedy and take more than its share).
Anyway, one realm might send a raiding party into another's resource area. In this case, the "raiding party" label genuinely applies. The party's goal is to take the realm's guards by surprise, defeat them, grab some resources and high-tail it out of there before the guards' alarm brings in more opponent players than you can handle.
Though there is adventuring far from resource areas, much of the game's PvE content is situated near resources to enable just this sort of harvest-guard-raid-conquer gameplay.
The Bounty card
In Catan, this one grants the player two free resources of his or her choice from the bank.
In an MMO, there might be resource drops from boss mobs or other PvE encounters. They don't supply enough of any resource to undercut the Realm-vs-Realm gameplay, but enough to act as a bonus. Such drops may be determined by semi-random loot tables, so a particular PvE encounter might offer ore one time and only weapons and armor the next.
There are probably a number of interesting ways to mimick the Bounty card.
DESTRUCTIBLE ROADS AND HOUSING
In Catan, each player spends resources to build roads, villages, and cities. A village gathers one resource card per roll (play the game and you'll understand) from the adjoining resource area. A city provides two resource cards per area (improved harvesting). Roads are built to lead between the villages and cities, with each road being exclusive to the player who owns it. You can't build along another player's road.
In the MMO concept, a realm must build on a resource area to harvest from it (or harvest in good quantities, at least). To harvest wool, you'll need shearing houses. To harvest ore, you'll need mines. The realm spends resources to build/purchase these buildings. In addition, guardhouses and other buildings may be built in the harvest area. When a particular combination of buildings are placed in the resource area, it moves from being an Outpost to a Colony. A Colony produces resources at a better rate (perhaps even better quality).
The catch is that competing realms may attack your Outpost or Colony and destroy the buildings (this system would require a lot of balancing, obviously). This is what makes holding a resource area and getting the most out of it difficult.
The MMO might even incorporate Catan's roads feature (though I have doubts about this feature's feasibility).
One possibility is that every realm builds the same type of road, allowing every realm to use the same roads. This way, a realm might attack and attempt to destroy a particular stretch of road because that stretch helps only the opponents.
Another possibility (more similar to the boardgame) is that each realm would transport resources differently, resulting in different kinds of roads... one realm's not useable by another realm. One race might carve a series of streams, which then act as waterways for small boats. Another might use raised stone roads, ala the Roman Empire, for carts pulled by hooved animals. A third realm might use animals with soft feet (like lions) and consequently build softer paths. A fourth might employ a magical hover system (imagine mine carts gliding over rail-tracks like boats).
In Catan, it's common for other players (realms) to refuse trade offers because you stole from them or your are too far ahead. In the MMO, too many raids on the same realm or controlling too many resource areas can result in lost opportunities or alliances against your realm.
Anyway, all of this is just off the top of my head, so I'm sure there are a number of problems in the design. But I can't help but think something roughly similar to this could be a ton of fun.