I have an idea for a third game.
As the Militia finish construction on Jack's new Titan, he sees his helmet start flashing due to BT attempting to communicate with him (that was the end credits scene). At first he is confused, but when he puts in on he hears BT's voice, confirming that he really is alive. Somehow (Respawn will find a way), Jack inserts BT into the new chassis, thus bringing him back. Or BT could stay in Jack's helmet and the new Titan keeps its AI, so Jack has two Titans assisting him.