Red 5 Studios CEO/COO Mark Kern, discussed their open world design for their MMO Shooter, Firefall on their forums.
The world will be seamless with the only loading that the players will see will be from changing channels and entering PvP matches. The world is a total of 10 square miles, with 2.5 being available at launch with the rest being covered by the Melding. He promises lots of missions and a variety of monsters with a plethora of dynamic events(large and small).
There will be no open world PvP, the game is strictly a cooperative experience with PvP being contained in arena style matches. Instances/Dungeons will not in the game at launch but they are testing prototypes and plan to release them next year. Last but not least, the total number of players per channel is around 300 but beta will help determine that final number.
I had the opportunity to play Firefall during Pax Prime, if you are curious about the game, head on over to my preview