I know that the old guy on the select screen is more than likely Shujinko, but I saw a thread that someone(forget his/her name) about it being either Shang Tsung or Shujinko. So here it is.
In the first Mortal Kombat, Shang Tsung was an old man but with pretty much the same morphing powers. After he was defeated and Shao Kahn granted him a new, younger body, Shang Tsung returned to Earth Realm to once again try to conquer it. So after another defeat at the hands by the hands of the mortals from Earth Realm, Kahn and Shang Tsung returned to Outworld.
They would return yet again, Kahn in the same form and Shang Tsung still in a younger body. But they would witness another defeat at the hands of the mortals from Earth Realm. Then as a new face came into the picture, the Sorcerer Quan Chi, Shang Tsung would watch him closely from Outworld. After Shinnok's defeat, and the his demise at the hands of Quan Chi, Shang Tsung new that Quan Chi could help him gain his immortality.
As Quan Chi returned from the Netherrealm and unlocked the Dragon King's Undefeatable Army, he formed an alliance with Shang Tsung to help revive the army. Shang Tsung and Quan Chi launched an attack on Shao Kahn, injuring him severely as to where Kahn had little power, as well as killing Liu Kang. They were successful in reviving the Dragon King's undefeatable army, but unfortunately for Shang Tsung, while Kahn's powers were too weak to keep him in his present body, he would age rapidly back to his former self. Betrayed by Quan Chi, he is at the mercy of the Dragon King.
It's just a theory. I would much rather that person be Shang Tsung, instead of Shujinko or whatever.