we’ve had many debates over theories for the H4 storyline and the enemies, ranging from precursors to forerunners and even including other human empires…
but i haven’t noted anyone talking about a possible return of the covenant, or - to be more precise - at least single species that were formerly part of the now defunct covenant.
recently hunter action figure boxes with the H4 logo on them were seen and yes, i “heard” bs_angels talking about “placeholders” BUT i can’t stop feeling like we’ll meet some old enemies again.
completely exchanging all enemies is a very dramatic step. after all, IMHO, the enemies we fought so far contributed a lot to halo’s success. fearless elites, brutal brutes, annoying drones, mighty hunters… even the little guys - though making the game feel even more “childish”, especially due to their squeaky voices - were part of the halo-identity and added to the walking tank feeling you should get when assuming the role of master chief, contrary to elites & brutes, although of course they made the gameplay more interesting.
due to the forerunner saga books and the forerunner setting seen in both the teaser and the concept art trailer, i’d say it’s save to assume that the flood will be back, but the flood alone would be boring and - btw: the flood need’s “food”, so there HAS to be someone else.
assuming that we, the reclaimer, don’t fight against forerunners & their technology (sentinels, enforcers & co), there has to be another enemy - but probably not precursors since “there’s no difference” (quoting the timeless one) between them and the flood.
that leaves us with the ex-covenant species, if there’s no new species introduced (crashed ship on installation 04 ?).
i haven’t read glasslands yet, but from what i get an elite-civil war is on it’s way and the brutes are still alive and kicking and despite them all bringing it onto themselves, they’re really pissed at mankind. i don’t see a motivational problem with sangheili or jiralhanae fighting “the Demon” again, question is: how could they be related to the “ancient enemy” and get to Master Chief’s legendary planet?
all assumptions, no proof whatsoever, just a feeling in my bladder.
i, for myself, would like to see some of the old fiends return - if the story sums up.