OK, here's how I see it going:
There will be LOTS of instances all the time and they will mostly be invisible to the player.
For starters, every player gets to select in what instance they will be playing - Single Player (SP), Friends-Only (FO) or All (FFA).
There will be loads of the first two types (with SP being optional as to whether the game interfaces with the central servers). No-one playing in SP or FO mode will ever see another player that they haven't approved.
Unless player-killer rules are breached, no-one in the FFA instance will ever see players from the FO instances.
So, before we even begin to address more than [insert number equal to or greater than 32 here] in the FFA instance, there will already be LOADS of instances created by player choice.
However, we will all be connecting to a central server running a simulation of one universe. There will not be "multiple server clusters" - the answer to Bungarus' quote on page one is also "NO" for ED. There will be one universe, but many instances within that universe.
The result of "multiple server clusters, each supporting a unique game universe" is many separate servers with no interaction (beyond chat) between characters on each "world".
The games listed, EverQuest, WoW...etc, all contain a fairly static world which very rarely changes due to player interaction with it and is hosted on different "login" servers.
Your character only exists on one server in a multiverse of identical "worlds", influencing very little.
In ED, everyone will be in the same, single universe, albeit instanced thru player choice or technical requirements.
How will this work for "unique" objects, will you see a piece of space debris you were about to scoop up disappear before your eyes because someone in an alternate instance got there first?
I really don't know. I'm not designing the game, just going on what's been confirmed.