Being a no sub required B2P game this is definitely nowhere near 10 million active but their E3 trailer is talking about the 10 million number for the first time that I've seen. The PC NA server is definitely hopping though and if you level a new character and do random dungeon PUGs you will see a lot of players brand new to the game.
They are also previewing what seems to be a couple of new dungeons in upcoming DLC: Horns of the Reach and Clockwork City.
“That's how the madness of the world tries to colonize you: from the outside in, forcing you to live in its reality.”
― Jeff VanderMeer