Got some more info about forerunners combat skins from one of the halo wikia
http://halo.wikia.com/wiki/Combat_Skin
Nice quote from the link
Very little is known about the Forerunner Combat Skin other than that it was used by combat personnel and was comparable to, but far more advanced than, the UNSC MJOLNIR Powered Assault Armor. It is first mentioned by 343 Guilty Spark as he is leading John-117 through the Library, wondering why he had brought "such ineffective weapons" to combat the Flood. He notes that the MJOLNIR is ill-suited to combat the Flood, and recommends that he upgrade to a Class 12 Combat Skin from the MJOLNIR, which is ranked on the Forerunner classification system as a Class 2. On the other hand, Guilty Spark also notes that the MJOLNIR will serve John well when the Flood begins converting Halo's atmosphere, commenting that he is a "good planner" Upon learning that there was a powered armor system six times more powerful than the MJOLNIR, John expressed enthusiasm at the opportunity to wear one
Concept art of a forerunner combat skin?
And the mjolnir suit being modulair halo reach modules i could see them upgraded the suit kinda like a modular mech game so to say. singleplayer will have multiple modules multiplayer will act more like reach except no armor lock
And prehistoric humans were old enemies of the forerunners Halo:Cryptum kinda logic bomb the whole universe oke atleast adds a whole new time era for games to go for. And make Halo a franchise can easily go on for 2~3 more console generations if handled well.
So the triangle would be Forerunner vs humans vs Some other form of flood mendicant bias the ai that joined the flood could bring in robot kind of enemies so a cybernetic kind of enemies part flood part forerunner robot tech.