Some people would not use it, others would use it all the time. The Ingame RP forum is -supposed- to be used this way, but it feels distant from the game. More people would use it if it was in the game. There are many features that are in the game now that I do not use, and think are bothersome, but it is not up to one side to decide what features the other side should have.
On consideration, the way the 'questbook' is set up may be a good model to start with. A play could add their own notes, but also, quest leaders could add 'world' notes as well.
Now comes the big question of who gets to set up quests or events. Everyone? Hmmm.... No. There would have to be some sort of limits based on quest type and duration. And also on the actual ability to run a quest or event. But who should decide this?
I suggest the people, and GMs. The players of the game will quickly come to realise who is good at setting up RPs. This is often proven by the "You should be a GM" statment. What I suggest, is that players can give each other limited amounts of 'RP' points (GMs could give out -or take away- unlimited points) that could be spent to access certain features of the Quest system, including rewards, board postings, NPC use and scripting, and even mob control if you have enough points. This would be a self regulating system, as no one would support a bad RP for long.
Of course limits and restrictions would have to put in place to ensure the an unskilled (in RP) n00b could not get all his buddies to dump points on him for his l33t qu3st. This means GMs would be able to delete any quest. Perhaps the number of RP points you could give out would be based on those that you already possess. One good roleplayer can easily see another. Also, players could not give points to others who had just given them points. If you join in an RP, you could continue to give points to the leader if you liked the RP. This way, those RPs that people lost intrest in would simply die out.
That is a very rough plan of what it could be like.