But there's always a catch 22 here. Yeah, you can support that many online, but then it's not an MMO.
Then no MMO except Eve Online is MMO. Unless I am mistaken, no other game has over 2000 players online in the same world in the same time, more like 500-1000.
Now, I'm no server expert, but if Valve has trouble running 32 players in the same game without severe lag, I don't know how indies think they have a prayer of supporting upwards of 1000 in the same game.
In FPS, one who wins is only about the ping, so it has to be as small as possible. In MMORPG, on the other hand, 100ms is enough for all playing situations, 500ms is enough for most but might seem a little laggy, and even lag of 2000ms would be enough for everything else than fighting. After all, most players will be either walking around, marketing or chatting.
Global chat channels and auction houses are good features lag-wise, because that means there are not certain places, such as pvp arenas or town centra, into which people will be collecting to sosialize. If map terrains are saved locally, only thing to be sent about the surrounding world is information of the nearby actors and their actions.
Many years ago people could not even dream of server hardware which is possible to obtain for $1000 today, yet there were UO, EQ and Tibia.