I think it's just a matter of showing Take-Two Interactive (Rockstar's parent company) that there is still a high demand. I strongly believe that there is still a desire to make a new Manhunt game within at least one of Rockstar Game's many studios.
I don't agree I think there are a number of valid reasons (both creatively and financially) that this game can and should still happen. I think most fans have given up any hope of a new entry in this series ever seeing the light of day. Manhunt, a video game created by developer Rockstar Games and released in 2003, has seemingly come to an end after 2007's lackluster sequel Manhunt 2 (which I personally loved).