I think they should make a new game. Here is the plot I've thought up. 10 years after the Halo event, both the elites and humans are happy with their current state of life. Nearly everything is rebuilt, save the barren hillside. Colonel Hood has died and the Arbiter is making a visit to earth. 10 days after his arrival, they receive a transmission from the most unlikely of sources. John-117. The master chief had said this "This is Spartan-117, can anybody read me over? I have news that everyone needs to hear"
Lieutenant General Illana Young replies "Chief?! You're supposed to be dead? How... what?!" Chief" I'll explain later, meanwhile help me welcome to FORERUNNER back to their one of their former planets. The Forerunner decided to self-impose exile to defend their race from any forms of life excluding their descendants that might try to disturb them, such as all the species of the Covenant. I just thought up that maybe to covenant rejoined in order to finally destroy the humans because of their love for the Rings, ark and finally their leaders. Fuelled by a fiery vengeance, the brutes, skirmishers, grunts, buggers, jackals, hunters and even covenant Hierachs with shield generators mistakenly attack the forerunner because they look almost identical to humans. The chief is joined by several other forerunner to fight off the covenant. The Forerunner saw how the chiefs suit had served him well in combat and decided to not only fix it for him, but to make copies of it. So now, there are 5 spartans ready to take down the covenant. The forerunner spartans names were
Taruk
Ruyan
Xylas
Bielks