When I look at the various game design ideas I've had, brain-dumped in the "Clearing some Headspace" posts, a lot of them were less about the kind of game I'd like to play and more about how to deal with the "endgame".
To me the whole concept of endgame is meaningless. To me, you play the game and if you hit a point where there's nothing left for your character to do then you stop. However I'm pretty much a 100% explorer on the Bartle scale, and to me, exploring doesn't mean just walking through a zone. The easiest way to do that would be the race to max level and walk through grey zones. To me, exploring a zone involves seeing what it's like to level through on a troll warrior. A troll shaman, if it gave a different experience, would be a whole new exploration. Also a troll shaman doing a level 30 class armor quest might be a different exploration (of the game) than a barb shaman even though they were the same quests, depending on where the quest took them. And of course levelling through the barb starting areas would feel very different (hopefully).
So for someone like me Everquest was close to perfect. There were a lot of races with their own starting areas and i liked (or didn't dislike) most of them and there were a lot of classes and i liked (or didn't dislike) most of them so I had maybe 60+ combinations most of which i levelled up to level 20 or 30 at some time over the years I played. Also the zones were designed in a much more open and non-linear way than many of the new games so the "exploration" of a lowbie zone as a troll warrior or shaman meant something different because you had different levelling routes to choose from and part of the exploration (of the game, not the physicla landscape) was to find the best route for the class in that zone.
So that was great for me - no worries about "endgame" in Everquest because i never got anywhere near it.
Other people did though.
Eventually games with progression run out of road. A single player game aims for the road to run out at the climax of the story and end there but mmorpgs don't have that luxury. People level up and eventually they reach the end of the road and have to stop. Some people do this very fast. Some people have more or less the opposite mentality to me and want to get to max level as fast as they can. Which on its own would be fine. However when they get to max level they don't just say "i beat the game" and leave, they tantrum on the game forums about lack of endgame content until the devs give in.
However you can't blame the max level racers entirely as all they do is highlight the problem early. Most of the average players will be a mixture and they'll be partly levelling and sooner or later they'll all be congregated at max level. So what can a game do?
The traditional method in PvE games is to add more road through expansions and "raiding". However both of these methods can eventually lead to making the problem worse in various ways. One way is they both usually add better gear which means previously top level gear gets dumped on the market and more level 30s are running around in level 50 gear and more level 10s in level 30 gear. This makes the lower levels, even those who are only levelling casually, start to progress much faster.
At the same time new max levellers just starting the game have a longer journey to cap and start complaining about the speed of getting there. Also raiding drills down on any min-maxing imbalance so players begin to start new characters purely for the endgame - for example their human warrior wasn't good enough for their raiding guild so they so they start an ogre instead. However these characters are not started for fun, they are purely started for the endgame and now everything in between level 1 and max level is a "grind".
So what happens is the average levelling speed goes up for the non speed levellers but still not enough for the endgamers and they want it speeded up more, which if they succeed makes the problem worse again. Further expansions gradually add to ever-quickening pace and no matter how much content gets added too many of the player base gets to the end faster than new content can be created and wants feeding more content. I can imagine a lot of game developers on the long running games eventually getting nightmares about it.
I think one possible solution to this for a leveled PvE game is to split the game into completely separate chunks. For example you start initially with a 1-50 game and people gradually start arriving at 50 and moaning. Instead of creating a new level cap and adding more content on top of the existing content, create a one way portal to a separate realm where the level cap is raised. If it's a fantasy game with gods then the obvious choice would be something like Everquest's Planes of Power where the players are summoned by their god to fight for them. Apart from ensuring the expansion couldn't mess up the balance you're trying to create in the original game something like this is easier to develop in many ways as things don't neccessarily have to make any sense e.g a self-contained plane of chaos created by a god of chaos could literally have anything in it.
A lot of the players who go through the portal would probably level up another character to 50 in the "Old World" but also players who got to 60 in the new world would be able to create new level 50s to try out without having to level all the way from 1 if they didn't want. After 2-3 expansions the level cap would be at 70 or 80 and you could let new players start characters at either 1 or 50. The original world could have content gaps filled and be bug-fixed, balanced and polished to perfection completely unaffected by the "endgame" which would keep happy those players who liked the original game.
The second solution to the endgame nightmare is PvP. It could be the clanbox variety where the players decide on the teams or the RvR variety where the game decides the teams but either way PVP provides the potential to soak up infinite amounts of player hours as they fight each other. It's also extremely cheap content hence why so many games seem to want to go in this direction. Not everyone likes PvP, especially not all the time, but it's definitely an option and it also provides a clue to the third option, for in essence what PvP is, is dynamic player-generated content.
So the third solution to the endgame content nightmare may be to somehow have the PvE endgame content player generated and/or dynamic as that's going to be the only way long-term a game could create enough content to keep people busy. How to do that? I don't know plus this has gone on too long but I think it's definitely one way out of these games gradually eating themselves through expansions.