Silver Surfer confirmed, and Galactus strongly hinted at in an eventhub article (http://www.eventhubs.com/news/2010/j...om-3/#comments)
The photo was taken by Denjetsu, who apparently snapped it while reading an article that has an interview with Ryota Niitsuma, MvC3's producer. Here are a few other points he went on to add from the write up.
• Niitsuma runs through the playable Fantastic Four cast of Doctor Doom, Super-Skrull, and now Silver Surfer, who will be shown off later this month. There are no screens of Silver Surfer yet, just a little portrait along with the other two fighters from that series.
• Silver Surfer is very quick and has a unique playstyle. He never stands on the ground, instead he's always hovering on his board, and he's recommended for advanced players. Doctor Doom was suggested as a good place to start for Fantastic Four fans who are new to the Vs. series.
• They've added more attacks from the Invisible Woman to Super-Skrull since the last public build.
• Also, Niitsuma mentioned that the Fantastic Four play a major role within the basic plotline of arcade mode, and that the final boss should be familiar to fans of that series.