Black Mask is perfect because we need a challenge for Bruce Wayne this time around as much as Batman needs a challenge. Roman Sionis v Bruce Wayne / Black Mask v Batman.
And also, I think with all these mobsters dead and gone, we need someone to combine all of the gangs together, and Black Mask is perfect for that aspect as well, as shown in Batman: Under the Red Hood.
Riddler, I could see him being a solo villain and not working with the mob(for once in Nolan's series).
And as for Mad Hatter; if there could be a way for Nolan to introduce more 'freaks', as in Penguin and even Killer Croc, that trifecta of villains would work really well, imo.