According to the dev, He only needs to finish the lance of Longinus mission and a final quest that would wrap up every story line. I don't think it would be so simple.
The only thing I can think of is that the protagonist will invite every mance to the city, The Vanderbills, the mafia, etc to his party with chanel, killing them off and showing his darkside, then we would know the truth of what happened to his parents.
But even that is hard to do, because a lot of these questline are far from finished. Moon, Sophia, Mia, Gem...Whatever the dev pulls off (If he ever do it) would be interesting to watch, even to see it all burn.