Thread Overlays Solution
I think experiences should be layered over the map and filled with things to discover or do, but these experiences should be accessible based on certain conditions, so that players would slowly uncover these experiences as they met those conditions. In a system like this, players would need to memorize hundreds of threads just to know everything that could happen to them. And even if they did memorize it would be pointless, because some of those things would likely never happen.
Furthermore, the unique experiences of each player triggered by individual threads should be designed to be so surprising, inspiring, or magical, that the player themselves would choose not to look anything up, for fear of ruining their experience.
Making Content Replayable
The idea here is that the game contains enough threads and scenarios so that no 2 play experiences will be the same, although those experiences may share similar components.
Once you reveal an NPC, sure you know that NPC exists, but you dont know everything about that NPC. One day, due to certain conditions, that NPC might reveal something to you that you never could have guessed which will add spice to that days adventure.
While you fight a particular monster, you may come across a mutation that occurs 1 in 1000 times which again, adds spice to what you are doing. The idea is that the game is constantly surprising you and leaving you scratching your head in wonder or challenging you with new experiences.
Experiencing Unique Threads
You could be having a conversation with a friend one day deep in a forest and one of you uses the /laugh emote, and suddenly an NPC pokes his head out of some tree stump to see what the commotion is. The NPC could then open up a whole range of actions.
The idea is to create many hundreds of threads that players can follow under certain conditions, so that they are encountering new threads of exploration at short intervals. Due to the conditions implied by some of these threads, such as perhaps being skill or time dependent, it would be very impractical for one player to experience every thread in the game in less than several years.
Furthermore, when you introduce other players into the mix, each player can further create other unique combinations that activate certain threads further adding to the magic of the game.
For example if you travel with your friend with lvl 50+ bard skill and happen to pass a minstrel sitting under a tree that heals stamina, that minstrel who normally seems rather boring, might suddenly spring up and request a duet with your friend the bard which not only heals stamina but now grants you an extra buff. Then, using the /dance emote (which you learned from a dance instructor) while they perform the duet , might cause the music tempo (and your dancing to increase), increasing the extra buff
An experience like this requires:
1. a friend in your party lvl 50+ Bard
2. lvl 5 dancing skill
3. passing by a minstrel
These are conditions which are not really uncommon to come across, but they add excitement and wonder.
It also changes patterns of gameplay. The next time you go to battle, you will call your bard friend and maybe your whole guild to come dance under the tree while your bard friends and the NPC minstrel perform a concert.
The idea is that these moments of wonder and excitement will be so precious to players, that they will treasure them and not desire to ruin any future experiences by googling every possible thread in the game.
Emotional Bonds with NPCS
This is the feeling I think an MMORPG should evoke.
Not a feeling of
"damn this quest is boring, but i really need that xp and gear i was promised by the random villager with the question mark"
but rather
"Samuel the Farmer who gave me 10 bottles of milk for free when i was dying, said he was attacked by bandits and lost something important and he's willing to impart with something precious if I get it back, i wonder what that precious thing is and I'd really like to help him since he was attacked and I'm really grateful for that free milk."