Jaffe. You really shouldn't be posting images of secret internal emails on your blog, even if you have applied heavy blurring to some of the more pertinent sections. Now we know your dark secret: your next game will involve cars. That's right, some photoshop whizz managed to see through the image's blurred section -- which probably explains why Jaffe has replaced the blurring with solid chunks of red, but the damage has already been done.
The super secret information does indeed reveal that the game involves cars, as evident from the lines "dragging him behind your car" and "when he is launched out of a car." The email also states that character animation for the "human characters" needs improvement because "right now it's so dry, it needs to feel like an action movie." Cars and humans? This game is going to be awesome.
All joking aside, this could indicate that Jaffe is currently working on a Twisted Metal sequel. Or it could not. It could be another car game entirely. With human characters. The blog post mentions a big milestone at the end of the month, which may mean we'll be seeing whatever game this is at E3 in early June.