I think the Forge of the Gods is going to be something like the VoG, but is a place where gods are born. The storyline might go that the cabal are forging gods(like atheon and crota) and the guardians must destroy the forge to stop the creation of these cabal super soldiers(their gods) . The raid could have parts where you hold areas(lets say while the ghosts sabotage their systems or wire up bombs) and parts where youre travelling through the cabal Forge. It could even take place on a massive spaceship or something and you start by crashing through the side and fighting off the labdig craft. The final battle may be more puzzle-like, where all 6 player have to be in certain spots to trigger the bombs/viruses from before. It would end not just with the death of a boss, but the forge crashing down around the team with a sprint to a waiting craft which takes the guardians back to their ships.