Whatever they choose to do

  Whatever they choose to do, they have to walk a fine line. Procedural content sounds awesome, but the risk factor is high because players will NOT enjoy running a dungeon that is different every time. Players who continue to subscribe to runescape do so because they know what to expect in a given run, and are continually mastering their own abilities to move through that content faster and more efficiently, so that they can run more things more often.

Adding in rare bosses to 5-mans will result in those rare bosses being ignored (the most recent example I can think of is how much of the Zul Cata-revamps were just... just touched by a majority of groups). Adding in multiple and changing paths will only create frustration in trying to find the end boss. Randomized abilities would frustrate both the tank and healer because they wouldn't know what to expect or how to plan the fight.

However, one brilliant area for procedural content would be solo scenarios. Achieving the same tasks in areas that are differently arranged with different things to kill with different abilities which you can handle by yourself without worrying about other people. Or even 3-man scenarios, by creating different pathing functions or rotating different groups of enemies. Because the goal in a scenario is to stay alive and kill things, there is less stress on group coordination.

--player-created content

Ideally, a great idea, but would fail for many of the reasons already stated ("the phallis imperative" let's call it). Quality control would be difficult to manage. They would have to establish a rating system and have to micromanage player creations to moderate for issues, and they already have so many problems in their core game ("tens of thousands of bugs", according to Street).

However, if players were allowed to create content by way of modular decisions, that might work and might be really fun (although it would need to make sense in the lore). An immediate solution would to be work with the garrison concept. Players establish a base, which is connected with a dungeon. It is specific to each player. You design the overall structure of the base, by choosing a specific blueprint that already exists (say from a list of 5-10 different blueprints).

Then you go around and recruit NPCs or capture monsters to inhabit your base. You choose where each goes, and a pathing is created based on where you have placed them. You train them, completing quests for your NPCs or mobs, finding them gear, raising their levels/capacity. Depending on the NPCs/mobs you recruit, there will be different quests. While in WoD, followers in garrisons can travel to actual dungeon hubs to gain loot, in the base model you could go with several of your followers or even other players and invade other player bases in order to capture resources that are necessary to build your own base. Just like flagging yourself for PvP, you could flag your base for invasion, and once you have flagged your base you will be able to invade other bases. But how would you actually invade other bases?

Once you have flagged your base for invasion, the game creates a map and puts that map into your inventory. You could then place that map for sale on the Auction House. Each map generated would have a certain ilvl based on the rough ilvl of your followers and the gear they currently use/training level of the mobs you have recruited. Hence, a loot table is automatically created from the loot your NPCs carry or a random loot table is created from the training level of your monsters. You can sell the maps on the Auction House (decide on the price based on the ilvl you are providing).

In addition, you can purchase other player maps. Once you have the map, you can activate to travel to that created instance with the followers you have selected to be with you (in a similar UI as your pet battle team). The follower battle team would be from top to bottom, so if you are not grouped with any other player, the four followers you have picked would join you, but if you were grouped with another player, only the top three followers would join you, and so on.

Once you went into that dungeon, you would have an opportunity to get the loot of the enemies that player equipped them with, as well as a chance to get random ilvl loot based on the ilvl of that map.

This solutions seems elegant and simple to implement. It requires a new UI, as well as an enhanced garrison, but besides that doesn't really get in the way of the world that Blizzard has tried to create.