LAYERING EXPLAINED
I'm exhausted from explaining this shit on the Classic WoW subreddit, so I'm putting this here now for anyone that doesn't quite understand what it is and why they're doing it. Numbers may be off but they illustrate what I'm trying to say.
Vanilla WoW servers held ~3k people. This was not a design decision; they simply did not have the technology to make it higher. Classic servers will have a much higher population cap, let's say 12,000, but for the first few weeks, these servers will contain layers. A layer is an instance of the whole game world that contains around as many people as an original vanilla server. Over the weeks after launch, after the initial surge is over, the people who got a taste and didn't like it have quit, and the players who are sticking around have spread out beyond the starting zones, they will gradually reduce the number of layers and increase the number of people on each, until the population has settled, and there's only one layer per server.
In retail, they've used sharding previously. Ignore any fucking dumbass who says "layering is just sharding renamed", they don't understand it and they're just fearmongering. Sharding is cross-realm and zone specific with a much lower player count. It's shit, they know it's shit, and it's one of the main reasons they've come up with layering instead.
Now, back to layers. Layers are not fixed. You log in and are assigned a layer at the time. You do not need to worry about not being able to see your friends, if you join their group and you're not already on their layer, you will move to it. Guilds will be on the same layer. Because each layer will be the size of a vanilla server, it's not going to be a big deal. So why are they doing it in the first place? Well, as mentioned above, people are going to try classic and then quit. They need to protect against that using a method that hasn't proven to be bad in the past. So, let's take a look.
Why not just have low population servers with no layers? A chunk of the player base leaves, and they will, suddenly you have a dead server with 500 people on and everyone else moves server or quits.
Why not just have high population servers with no layers? Imagine 300 people in a starting zone competing for a few mobs. Dumb, frustrating, but funny and a true launch experience. Now imagine 1200 people. Not funny, just unplayable for most people.
Why not just merge low pop servers or character transfers after a while? They've done this before and it's not good for the server. It fucks up raid teams, and thus guilds, and thus friendships. Server merges, suddenly player X from guild 1 wants to join hot new guild 2 who are better than guild 1, and so on. Bad.
Again, the main point is that this is temporary. The WoW GM has gone on record yesterday as saying that it'll be eliminated over the weeks after launch, absolutely before phase 2.