Blizzard started a stress test for Classic yesterday, where anyone in NA with a WoW subscription could try Classic. The servers will be up for a day or two, if you didn't get to try Classic out.
I found the test quite funny. Blizzard was clearly testing their server stability, as they put way too many people in the zone for game-play purposes. I made a mage, and I had a lot of trouble finishing the very first quest. I'd start casting a Fireball at a kobold, and someone would tag it before the cast finished.
In the end, I resorted to running up to the kobold, hitting it with my staff to tag it, and only then start casting Fireballs.
The conversation in the zone was very lively, and everyone was remarking how this was totally unlike retail servers where it's silent. That's true, but the Beta servers were like that at the start, and now they're dead silent.
If I was making an MMO, I would strongly consider adding a world chat channel that everyone on the server is in. There's a critical mass of people necessary to get chat going. For zone chat, it really only exists in the starting zones, and really only at launch.
Or maybe, like Blizzard is having layers for the world, have "layers" for chat that expand and contract depending on the number of people. Maybe the game starts with one chat for the starting zone, and all the other zones have the same chat. Then as people starting levelling up, maybe the first two zones share the same chat, and so on.