Could Gerard potentially be a new hero..? It seems like a no but there is a little evidence.
Most overwatch heroes were Though of as Dead at some point, for example : Jack morrison/ Soldier: 76 was presumed killed in a Battle Ana was thought dead after her confrontation with Widowmaker And Reaper is, honestly, still Close to dead.
Maybe he survived somehow, maybe overwatch brought him back to life via technology Mercy uses to Russerect. Theres also a Security guard in the Emblem with many Unannounced OW heroes (Hes next to the omnic with the Athena symbol, and a little blurry). He could be gerard, as he Does have Overwatch-style blue armor. He does not look like the Gerard in the "Wedding" spray Widowmaker has, but he might have changed a little.
Its a Far out theory but there might be some more Evidence.