Firstly, allow me to comment on the state of the main & supporting quest line.
I think that it’s quite good. The way it is now, it’s very easy to find a party that’s doing the same thing as you are. If you’re in Map A, chances are, you’re doing Quest A. You are already grouped together with people trying to do the same thing as you. This lets you meet players around your level, people you can party up with and possibly see again when you move on to the next area.
This leads me to my problem.
Unless you’ve coincidentally run into a player who is leveling their alt character, it’s very hard to learn about the game or what to do. Yes, you could just read up online about the game, but that breaks immersion. It also removes interaction between players. If I wanted to ask another player a question, chances are, they will not be any more experienced than I am.
This leads to many potential solutions.
The most popular I think, is backtracking. Give higher leveled players a reason to come back to lower leveled areas. This gives new players the chance to see cool skills so that they can see what they might want to be in the future. They could ask questions and get answers, make friends, play more actively, blah, blah, you get the idea. This hurts the main quest line perk, however. Not everyone you meet is someone you can potentially party with. Higher leveled characters are also not always able to help you if they haven’t played with your class.
This leads to my solution, class quests. Introduce quests only players of that quest can do. Put the quest master near the class instructor so that you have a bunch of players with similar questions but of varying experience levels. A level 30 Wizard could easily answer a level 20 Wizard’s questions while they’re nearby. They may even be able to party, since players converging around their class instructor will likely be of similar levels. This also has the advantage of giving people playing a second character something new to do. If I make a second character, I’m still playing through the same quest line, reading the same text, exploring the same maps, for the second time. The only thing that changes is that I’m using different skills to fight with. Having access to an alternative short quest line can offer a breath of fresh air to a second playthrough.
To summarize: Current quests are good at getting similarly leveled players together. Which is good for parties, but not ideal for the community. Adding class-locked quests adds flavor to each class while also connecting players who like the same thing, but of different experience levels.