It will come eventually, need to get all the other content first, since your gonna need the Empress equipment and for those playing the "Tank" will need Vaal Hazak Gamma in their builds.

Even if you had it now, NOBODY would be able to finish it. The armours, decorations, player skill required to hunt Behemoth isn't here and it will not only frustrate some players, it might make some of them quit. Behemoth's HR requirement is a hilarious HR16 and there are players with HR 10 times that who have still failed to kill Behemoth 30 runs in.

Hopefully they will roll out dlc at a daster pace than the console