I have no idea if this was mention for Halo 5 forge, but I think if there is forge that you should be able to make A.I.'s in forge! You could spawn A.I.s in forge and then in custom games you could fight them.
It wouldn't be hard to transfer campaign A.I. ability into forge. Wouldn't that be cool?
You could make videos of A.I.s fighting each other and players be on teams and it could be a war on halo. People could make You-tube videos or something of the sort and people could watch epic battles in progress.
So if they make A.I.s in forge, they will have made a game I will totally enjoy 24/7!