here a nice article that might answer a view questions:
1. You can deliver an AAA MMO with a B2P model.
2. Remove the fight over resources in the PvE world.
3. Play with who you want, when you want, how you want.
4. Mass PvP is better when it's bigger.
5. Have a relatively low power ceiling, then go for horizontal expansion.
6. MMO PvP can be done as an E-Sport.
7. It's not what you play with, it's who you play with.
8. The controls of an MMO with the abilities of a MOBA and the physical interactions of an FPS. With a pinch of Magic the Gathering.
9. Try and have the best soundtrack ever in an MMORPG
The Tao of Arenanet - CLICK ME