First off: I did not read the essay.
Now...
I am sure that massively multiplayer games are indeed for newbies in the way I think the essay explains it.
Just one thing I wish to add: If you take away the massively, you are left with things that are actually tolerable.
A good example are some of the better persistent worlds of NWN. The best have permanent death (as it should be), other good ones have harsh XP penalties on death (33% of total XP, all gold, all equipment). Such servers usually enforce RP and are run by experienced DMs with an age that is usually around 30. Thus, they actually provide immersive quests and interesting playing experiences. The server I was on was low level, too, a big plus for it actually means that level 5 is quite powerful indeed, as it should be in D&D.
The best example for a Codex-friendly multiplayer game that I know about is Armageddon. I have mentioned it quite often now, even though my limited time does not allow me to play there anymore. It is a MUCK, which means there are no distracting graphics. Let me once again mention the features:
* harsh, gritty, Dark Sun-esque world
* players can and will change the game world all the time
* permanent death. Yes. A good thing. Once you die, you die. The harshness of the world means that one might very well be killed by another player for a bit of water or a handful of coins.
* danger. Intrigue. Despair. Choices and consequences (yes, yes). Players have power, and use it. If they live long enough to amass that power, that is.
* newbie-unfriendliness. A good feature, in my opinion. While there is help in written form available, NO ONE will be nicer to someone ICly just because he is new. In fact...
* NO OOC. NO METAGAMING. AT ALL. NONE.
* players that can type and write. And write well.
* well-written room descriptions.
There you have it. What could a Codexer dislike about a game like this? Thus my point stands: the idea of a multiplayer game is not inherently bad, but once you allow the 90% of morons with an internet connection to play them too, they suddenly turn into stupid money and time sinks that reward patience, not skill.