I think it would be lovely if we could all live happily in one big world together (by type of world, as frinka said), but several million people all together would have severe consequences. For example, there would be the funsuckers, but they always ruin it for everyone anyway. Cuppy from CuppyVille also mentioned the issues with names. So few people would get the names they wanted, and character names are important.
A lot of responses to this shared topic (you can see links to people's blog posts in the Blog Azeroth forums
) mention how their computers wouldn't be able to handle all of the people in one place. That would of course have to be worked out, but several games are doing this already. Star Wars: The Old Republic
is one of many MMOs that instances high-population areas. So at any one time, you will never share a zone with more people than you can handle -- unless they are all standing on top of each other. If your friends are in another instance, you can join them easily. So if you are in Orgrimmar-12 and want to hang with someone in Orgrimmar-7, it's a simple matter to do so.
Player-run events like the ones we have in It came from the Blog
(shameless plug!) would have difficulties. We might not be able to get everyone in the same instance, which would make the event pointless. On the other hand, people would be able to join us from all over the region with their mains, which would make the events even more fun.
I think Blizzard is going in the right direction with their cross-realm changes. From dungeons to questing, we have many ways that we can play together. All we need is cross-realm guilds
, and I think we'll be golden.