As you may or may not know, Rockstar plans to continue the story of Michael, Franklin and Trevor (which I guess means that "The Third Way" is cannon and the options to kill Michael or Trevor are not). I assume that theu would use the funds from the union depository heists to pull off more stunts and make more enemies.
Something I'd like to see is the return of either Niko or Luis as supporting characters. What are your ideas? I'm also curious as to how its going to be layed out. I mean after you've downloaded it will you be given the option to load the DLC rather than the regular story (like selecting online by pressing X or A except it would be something like Square or X)