Mmorpg like? Monthly costs? Digital release only?
MMO-ish would make sense -- based on the screens, it doesn't appear that they've upgraded the graphics or world design significantly from the previous game. Maybe they spent most of their development with MMO stuff; quests, online functionality with lots of other players, etc. Also, the blurred out text next to the logos in the background of the first picture might indicate some sort of faction/guild system?
Since the games have had such huge worlds, lots of different vehicles and stuff, maybe they thought it'd be easy to turn it into an MMO. If they implement a decent quest or mission system it might be fun for some people. Unfortunately, then it'd just be another "MMO" with, I assume, some fun mechanics, if they manage to implement the grappling hook and parachute, or similar mechanics.
Part of the reason why I liked Just Cause 2 so much was because it had a huge world for you to play around in with some awesome mechanics -- and, while MMO's tend to have huge worlds, they rarely have interesting or varied mechanics (Probably because of possible delays due to ping, as well as the general game design of an MMO -- playing with so many people requires structured and streamlined game design and progression in order to make it rewarding for everyone.), and it's just not the same when availability of the game is dependent on servers hosted by the publisher/developer.
If they are indeed going with an online type of solution, then I really doubt they'd expand on the very unique mechanics in the previous games, which is what I was hoping for, along with a more detailed and varied world. Mechanics like a more complex grappling hook system, wires, a physic system, more destroyable objects, etc. would have been awesome.