I Think You Right !
In The Trial Of The Gods Co-Op Mode Video You See Hercules Jump Down To The Arena W/ The Nemean Cestus On And A Bit Later He Does Not Have 'Em On Any More, Maybe The Teammate Is Going To Locate It And Use 'Em To Defeat Hercules At The End Before The Gods Interupt The Fun .Laughs
Just A Guess But It Would Explain Why It Was Not Shown In The Video Of The Teammate Using It On Hercules .
I Have A Strong Feeling SSM Is Going To Add It .The Nemean Cestus Are BOSS .Lol
Long, Live, The Shade Legion Σκιά !
TLoU GotY 2013 .
People can stop guessing, the 4th weapon are Gauntlets and were confirmed by one of the Dev's an African American man, who was talking about the Multiplayer (On Youtube somewhere).
Hades - Hammers
Ares - Swords
Poseidon - Spears (Tridents)
Zeus - Gauntlets
Just_Tank and Gypsy did a Live Stream last month in May and Tank hinted that the 4th weapon would involve wrestling (using your hands and fists).