Remember how, in classic arcade games (Galaga, Pac-Man, even Mario Bros.), "levelling up" meant racking up enough points that you win an extra life?
This is an option for MMOs.
Trials of Ascension (which never made it to release, but had some good basic ideas) is the first MMO design I'm aware of to use a life-counter system. Delayed permadeath, you might call it. Characters would be allowed as many as 100 deaths before finally experiencing permadeath (which ToA helped to offset with lasting character impact on the gameworld and character artifacts).
What if the player started out with fewer lives, but could also gain extra lives through racking up points? The player's "score" would take the form of his or her character level, thereby acting like a "high score" ranking table. A high level could be considered a genuine accomplishment to be proud of.
In fact, what if character levels had nothing to do with skills and hp (at least, past a particular level)? What if levels were only about score and extra lives?
GIVING UP CONTROL
Of course, there's a notable difference between MMOs and arcade games that prevents current MMO models from making character levels more like player scores. Some might say levels are already used that way to some degree, but I think most players are more proud of the increased combat power that's associated with new levels than proud of the levels themselves. The troublesome difference between arcade games and MMOs is the player's degree of control over the game encounters.
In a classic arcade game, gameplay is about reaction. Sure, you might be making meaningful choices (like whether to pick up the Splash weapon or Laser in Contra), but you're limited to choosing between things that come to you... not you to them. The player is funneled down a particular path, encountering objects and events that the developer chose for the player to experience at that particular time. The player can only continue pushing forward, overcoming whatever obstacles present themselves, with no expectation of control over where the adventure will lead.
Because MMOs traditionally offer players much greater control over their adventures, the difficulty of levelling up can be determined largely by the player. I could challenge tough enemies, risking death but accruing greater experience-per-kill. Or I could take the easy road, levelling up slowly but safely by killing weaker enemies.
If we wanted levelling to act as a scoring system, we wouldn't want to reward people for tip-toeing their way to the highest scores. A fundamental change would have to be made to the traditional MMO model.
What comes to you
The change is one I would probably make even without this sort of scoring system: take control out of the player's hands.
I would offer some predictable content for a predictable length of playtime. But overall, let players experience adventure as it is in epic stories and all of the great novels they've read. Let them be faced with encounters they didn't choose or expect. Make it more like those classic arcade games in that your (the player's) control is more over what you do with the events thrown your way than over what events you experience.
I love open worlds. It's one of the main features that attracts me to the MMO genre. But being able to journey in any direction and not being bound to one storyline don't mean players must be able to select their game experiences as if from a fast-food menu.
In a less predictable world, players could still choose genres of adventure to suit their moods: urban market, jungle, horror, open sea, mountain trails, etc. They could also be aware of the general range of possible events which might occur in those places, like knowing what creatures inhabit the area. They just wouldn't be able to schedule encounters like they're boxing matches.
Anyway. Obviously, I could go on forever about making MMO worlds dynamic and unpredictable. But the point here is that it would be a necessary step if a developer was to make levels less about skills and power, more about longevity and prestige. I don't think such a system would always be the best way, but it seems like a good option.