I think the DU is simply the main character that was meant to be from the beginning. Clearly, he is connected to Bhaal and ties in well with the previous two chapters. Additionally, Tav has zero background, zero interaction in the game world (except for the class, but that applies to Origin characters as well), and is the least special character within the party. The DU, at the very least, has amnesia which justifies the lack of references to his past life and could/should have strong connections to the plot's ending.
