I think the Didact should bring an forerunner army with him to earth. Not sure if any other forerunners exist but it would be sweet. I would like to see more of them and I’m not talking about the Promethean Knights.
I dont think their are any others.
Personally i think the covies attack installation 03 since they know where it is now and try to activate it like old times, the didact finds out (he hates the halo’s) and learns what happened before he woke up with the covies and humans and how the covies got their tech from memorial bias and that the human even tho where fighting a lot of different races held their own and that the covies had that tech and were using engineers to maintain and still saves the galaxy from halo will make him gain some respect back for humanity and he may be forced to fight with them to stop it from firing.