I'm thinking the obvious one, is if Brock does appear, he does so in the Main Event to take out The Rock....or John Cena.
I know the rumours point to Rock vs Brock next year, but would having 2 part timers headlining really make sense? Brock vs Cena I think would make more sense, in regards to the current roster, they can't rely on the past 100%.
And on that same logic, if you bring Batista back, have him put over a guy like Sheamus.