I would like an MMO with several dozen actual GMs curating and generating story content and changing the world based on participation and outcomes of events
That's pretty much what a number of Neverwinter Nights servers were, considering the game even had built-in functionality for ingame GMs. And with the size/scope of some servers, it wasn't unheard of to have multiple GMs running their own separate things in different parts of the world.
I've had a concept banging around for a while, basically ever since I ended up stumbling upon the secret vampire hunt in Red Dead Redemption 2. The idea is to manage your own vampire-hunting guild/family, with permadeath for the characters but with new members available to take up the mantle of being the PC. Persistent advancement in the form of learning new facts about the various types of beastie you were going up against, which gets recorded in your archives. Similarly there'd have to be some sort of collective treasury that gets funded from these pursuits.
But basically you'd have to hunt down a variety of different pests, with varying behaviors and weaknesses depending on what exactly they were. And you'd have to determine what they were, or that there WAS something in that area, from the vague hints and clues you could get out of local gossip. Naturally, disappearances could be a local cult rather than your prey, and dead bodies could be the work of a perfectly mundane serial killer... But combined with other hints that indicated the MO of a particular vampire type you were looking for, you might have found yourself a useful lead.
The types themselves would be wildly different, some vampires being little more than bloodthirsty beasts preying on local peasants, while the older and more advanced ones could be hiding in plain sight in an urban center. More worryingly, the smart ones would be able to pick up on your snooping around after them and asking probing questions of the populace, if you weren't cautious about covering your tracks and keeping your intentions and identity under wraps.
The Witcher (3) was fun enough with its little hunts, but everything was scripted and designed, and once you'd played through them there wasn't anything more to be uncovered. Furthermore, you'd basically just be able to reload a quicksave and try again, not to mention being the amped-up supermutant that Geralt is. I like the threat of losing a unique character to permadeath, and of being more mundane man and less magi-engineered killing machine... More than that, I like the idea of this fragile, vulnerable soul being able to punch
way above his mortality class with the help of generations of accumulated knowledge on the specific fiends he's going up against, and the usage of cleverness and tools designed and prepared specially for this particular threat.
It's the middle of the night, so I'm not communicating all the particulars of this idea very well
There are plenty of things in my head that seem like cool details, but the gist of it really is just "Establish a vampire hunting guild through trial and error, use logic and preparation to track and eliminate your foes, be careful not to become the hunted rather than the hunter"
Pre-post edit:
Didn't some of the third party NWN servers do that? Which might be arguable on the 'MMO' definition, but it was still with double-digit groups.
Ninja'd