If it were possible, would you want Blizzard to put all characters in a single realm/game world by realm type -- PvP vs PvE vs RP? Why or why not?When I first started playing MMOs with Ultima Online, I was severely disappointed that we weren't all playing in the same world. It just seemed to me that it wasn't truly massively multiplayer if we weren't all playing together.
When Anarchy Online first began, they tried to keep it to one world but ended up creating a second one after a while. I really felt the single realm was a big part of what made the game unique. (It was the zoning that made me stop playing, though.)
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.
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.