One of the arguments I've heard recently in favor of allowing players to run multiple characters per server (MCS) is that it benefits Explorer players.
I'm not convinced of that... and I'm probably one of the more hardcore Explorers you'll ever run into. Looking at MCS with my wannabe game designer hat on, I see it more than anything else as an issue of gameplay balance. That makes it primarily an Achiever concern.
In a typical MMORPG that's balanced for a single character's abilities and resources, someone playing five or eight characters on one server who share resources (skills, inventory slots, etc.) as though they were a single character -- an "ubercharacter" -- will have a significant advantage over someone who (for whatever reason) runs a single character per server.
Why should someone who plays their (single) character like an actual character in the gameworld be disadvantaged versus a player who treats characters not as people but as tools for beating a game? Why should the game be designed to provide a multiple-character-per-server capability that's primarily going to be used by some gamers to crank out a bunch of alts that have no identity as characters themselves, but are only used as person-shaped boxes that provide free skills and resources to a main character?
This argument really has nothing to do with Explorers. Real Explorers seek to understand systems in depth purely for the satisfaction that deep understanding brings -- they aren't concerned with trying to map systems as rapidly as possible for direct gameplay advantage, which is an Achiever way of thinking.
More pointedly, if there really was anything to the "Explorers want multiple characters" argument, such players would be perfectly happy with creating multiple characters on different servers. That would provide the breadth of ways to experience a gameworld that the Explorer appreciates. Those who insist that they "need" multiple characters on the same server are far more likely to be Achievers, who know perfectly well that this will give them a scoring advantage in a MMORPG whose challenge level was (by design) balanced for single characters.
So finding an alternative to an unrestricted MCS design is not about helping players experience a MMORPG as a simulation (which is how Explorers want to see it) or as a drama (which is how the roleplay-focused Socializers prefer to see it). It's about finding a design that insures that the quality of an individual's play within the gameworld is what determines their results, as opposed to gaining advantage by using an outside-the-gameworld mechanic such as running multiple characters on one server. In other words, MCS versus SCS is a question of how best to design the challenge level of a game so that the rules-based, score-keeping part of the MMORPG is the most fun for the greatest number of potential subscribers.
So how do we get there? One thing I have to point out is that at the most fundamental level, making a game means designing rules that are fair -- if the rules structurally advantage some players but not others over the gameworld (or over other players), then it's not a good game. So saying "I need N characters per server" is perfectly valid from one person's individual perspective, but it can't be the whole story when you're trying to design a game whose rules fairly serve the interests of thousands of players. Unrestricted MCS fails that test because it creates an artificial gap between those who (for whatever reason) focus on playing a single character versus those who play multiple characters as one ubercharacter.
That said, let's look again (in a little more detail) at some alternatives to unrestricted MCS.
One obvious and simple hack (which is why developers started doing it years ago) is to tag some items as "no-trade" or "soulbound." This has the advantage of being relatively trivial to implement, but at the cost of being a blunt instrument: while it limits muling/twinking, it also artificially restricts useful exchanges of items between different players. That's undesirable in a gameworld that needs an active player economy.
An alternative to this would be a more targeted restriction against allowing any interactions among the characters owned by one account. This would mean (for example) no trading items between one account's characters, or using the resources (such as bank vaults or houses) of other characters on the same account. This would minimize muling/twinking by individual players without unnaturally interfering with useful economic interactions between different players. Unfortunately, it would do so at the price of adding more complexity to the game code, including a possibly tighter-than-usual linkage between gameplay capabilities and the billing system.
Another way to allow multiple characters on one server might be to design the game such that the level of challenge dynamically adjusts to the number of characters one actively plays on a particular server. Someone who plays a single character would enjoy the same risk/reward ratio as the player who switches back and forth between five characters as though they were a single character will five times the resources and skills a normal character is designed to have. Unfortunately, while this approach could improve the fairness of PvE play, it does nothing to level the PvP playing field.
The best approach may be the simplest: instead of tacking on artificial restrictions to economic exchanges, or developing complex heuristics to try to make unrestricted MCS fair, why not simply allow only one character per server?
The true Explorer who wants to study different aspects of the gameworld can create a different character on every server. The usual counterargument to this is "but roleplayers need to be able to pick different characters to play depending on the other characters in a group." (I suspect that this ostensibly RP-friendly argument is usually made not by roleplaying Socializers but by Achievers who have other reasons for wanting MCS. :P)
What's important to see here is that if everyone lives by the same one-character-per-server rule, then roleplaying friends can all create different characters on other servers as well. Picking which character to play just means agreeing on which server to play on that evening. (I'm not saying that's always an easy discussion, but it's no harder than the same discussion of who gets to run which characters on a single MCS server.)
One final note: I've also heard people say, "But if real MMORPG designers thought that running multiple characters like a single ubercharacter was wrong, they wouldn't permit us to create multiple characters per server." I agree. I'm not saying players are wrong for doing what game designers allow them to do. I'm saying game designers are hurting themselves by building their games to permit players to create multiple characters per server. Maybe the publishers force them to do that; I don't believe there is any valid design reason for allowing players to make gameplay challenges easier than intended by running multiple characters as though they were one unnaturally gifted character.
On balance, I think SCS is definitely the right way to go for a MMORPG that allows characters to learn (and unlearn) skills. For a class/level game, however, I recognize that people want to group with their friends but don't want to have to run the same character forever (or, at least, as long as all their friends all run their same characters). So some form of restricted MCS, such as restricting exchanges between characters on the same account, might be made to work for a class/level game. It's still something of a hack, but it would cut down on the majority of ubercharacter action without preventing useful economic activity between different players (as soulbinding does).
The main thing is to realize that unrestricted MCS, regardless of how many people say they "need" it, really is a problem of gameplay design. It makes the game easier than the designers intended. In short, unrestricted MCS makes a MMORPG less fun.
I hope those leaping to disagree with me on this will at least recognize that my purpose is honorable. I'm not trying to make MMORPGs less fun for them (by "taking away" features); I'm trying as best I can by my lights to make MMORPGs as fun as they can be by encouraging designs that don't supply features that unnecessarily undercut the carefully-designed balance of character abilities versus gameplay challenges.
Basically I'm looking for areas where MMORPG design can be improved. Does anyone believe that MMORPGs as currently designed are perfect and holy and must never be questioned?