If they are going for a Diablo based FPS game, I think it might be one of these options:
1. A single player experience that would attempt to rival the stature of Half Life
2. A survival fps game like ARK: Survival evolved
3. A death match based game like COD/BF
4. A mobs style fps game like OW
I think the first two options make more sense... Option 4 doesn't make sense at all.