http://www.mmogchart.com/ has good data on numbers of MMORPs users. The table says one thing: WOW is booming (green line). The numbers are from

June,

2006. The site has the actual excel numbers of many other games. Interesting data. By the way, according to video blogger (on Jan 11, 2007):

Blizzard Entertainment announced today that World of Warcraft, its subscription-based massively multiplayer online role-playing game (MMORPG), is now played by more than 8 million gamers around the world.

World of Warcraft has also achieved new regional subscriber milestones, with more than 2 million players in North America, more than 1.5 million players in Europe, and more than 3.5 million players in China.

So it is possible to build a massive MMORP for the metaverse. (well, baring in mind that true Metaverse is a bit more difficult).