I'm having trouble giving an opinion in this thread, so I'm just going to give my simple opinion. I'm all for implementing this system as I want to interact with more people and only grind for a few hours for a few levels rather than 10 hours for the same amount.
(Also, there is little skill in the time spent grinding. Pointing to musicians who practice their butts off as my counter example. Hours and hours of grinding for something with a very high skill ceiling, which maplestory does not possess )
New Edit:
Eherm! I would like to retract the above statement and make a different argument using anecdote and other things besides.
First of all, I'd like to take a gander at describing the future pool of players for this server (me being one of them only a few days ago). In that pool of potential players, I believe that there is a sizeable chunk of players that really want to feel that sense of world exploration and character growth that earlier versions of Maplestory had. There are several components in the game that contribute to that, but the one that's most pertinent to this discussion is the grinding.
Grinding, as much as I may dislike it, is one of the cores of that nostalgic feeling. I, for one, can attest to grinding's importance as I immediately dropped another server after reaching level 20 in like 30-40 minutes. There's no sense of worth or accomplishment in getting levels like that so easily, meaning that some of the grinding aspects are good. However, and a big however, grinding, in excess, can be a detriment to the enjoyment of the game. I think it's okay to grind for a few hours for a level when you're at level 75, but I don't think it's okay to grind for for an hour for a single level when you're at level 15, and that leads me to another topic, Maplestory's pay-to-win model. We already should know about this topic, so in short, in order to get players to fork out money, the designers purposely make leveling in the game extremely slow so that they can sell exp doublers. This pay-to-win aspect of vanilla Maplestory is not very fun, evident from this server's emphasize on banning pay-to-win items and with some probable changes. However, as I'm sitting at level 19 grinding my butt away as a new player, I can clearly see that those unenjoyable, frustrating systems are still in play.
...So, in essence, Maplestory was, in terms of progression, made purposely unbalanced, and the game is both better and worse for it. However, just because the game was made unbalanced in the first place doesn't mean we can't make changes that simultaneously preserves the nostalgia of the game and dampen the parts that make the game less enjoyable, and perhaps we can even improve upon those feelings.
So yeh to the party mechanic, and it doesn't hugely impact the people who prefer to go solo.