*Shrug* Why shouldn't it have two possible protagonists? The franchise has had one released game and one to-be-released game, so it's not exactly bucking a trend. Not every franchise has to have a singular central character which they follow across all the titles. The main Final Fantasy games have a different central cast each time, as does the Elder Scrolls series, Borderlands series, Bioshock series, Dragon Age series, Persona series, Dragon Quest series, Fire Emblem series, Disgaea series, the Assassin's Creed series (sorta)[footnote]This one's significantly iffier than the rest, but while Desmond was the nominal protagonist up until the end of AC3, in practice he and the Animus acted more as a vehicle to ease the audience into the roles of Altair, Ezio (who further complicated things by having two sequels of his own), Haytham, and Ratonhnhak?:ton rather than an actual focus character[/footnote], Silent Hill series...point being that there was no obligation to stick with Corvo and just Corvo. Hell, the DLC for Dishonored saw Daud as a focal charater, so adding to the central character roster certainly isn't out of left field, especially considering that the Outsider bestows his gifts on pretty much anyone who piques his interest.