This is not a normal suggestion. I feel, in someways I think it might belong in the lore section but this goes much much further then the in game lore.
One thing I find is the MSQ is so powerful and great that once it is finished I am wanting for more, but until the next patch that continues the story, its mainly just a dungeon grind for gear. I know there have been side stories but I am feeling like I would love to see something much more.
First this idea I have would require making this MMO part theme park and part sandbox. Now I know most think of sandbox as open world pvp; with players free to be as evil as they want, gank and grieve all they want etc. But that's not what a real sandbox is. It's players being able to create their own content within the parameters of the game.
My idea: Keep everything that we already have plus what ever you plan to add in the future story and quest wise.
This next part is where the meat of my idea is. First, I know there are many players who love to create extensive back stories for their characters, as I do. We may even go so far as to create our own stories outside of the game with our characters. My big crazy idea is to allow us to make our own stories within the game and to be able to create our own adventures and quests. This could be implemented not only with other players but with NPCs. They could have much higher AI as in games like Oblivion, and Sky Rim.
Also I have seen but don't remember the MMO that is in development where you can become friends with a NPC, help them with things and they in return will give you quests, and access to dungeons.
I know you as developers could take this further, where we could be able to relate our story to the npc and then we could go on adventures/quests with them. I know this would probably be a huge task and may not be able to do this due to production schedule, and future expansions already being worked on. But I think it is a worthy goal and could push this game way beyond any other MMO out there. I know it could make us creative story tellers very very happy.