Playing to their strengths, the movie is set in the world of organized crime.  From Reuters:

"Bob De Niro (and I) are talking about something that has to do with that world," Scorsese told reporters after a press screening of Shutter Island, where the audience reaction was decidedly muted.

"There's no doubt about that. We're working on something like that, but it's from the vantage point of older men looking back, none of this running around stuff."

De Niro has had some pretty bad movies in the last few years, but if anything can pull him out of a slump it would be a mobster picture with Scorsese.  

Scorsese's latest picture is Shutter Island, which premiered at the Berlin Film Festival over the weekend.  It teams him up with Leonardo DiCaprio for the fourth time, and also stars Mark Ruffalo, Sir Ben Kingsley, Jackie Earle Haley, Michelle Williams, Emily Mortimer and Max Von Sydow.  Shutter Island hits theatres February 19th.