so as the title points out, i've got a bunch of suggestions since i'm a massive halo nerd (srsly i could probably give the librarian a run for her money) AND i'm new to not only the SotP forums, but the entire base game as well. so keep in mind i don't have a damn clue about most previous topics about ideas and some stuff. so here goes:
could there be new factions after the forerunners? ala vanilla SotSE:Rs whole 2-pronged selection screen. for the UNSC there could be the United Rebel Front or more simply/universally, Insurrectionists, who would have access to all UNSC, older UNSC and some covenant technology (this is assuming the URF is the post-war and therefore, covenant species accepting version and not the pre-war variety) and would be more focused on sabotage, conversion/boarding, culture and overall offense than the UNSC. in other words, a general all around pain in the ass.
for the covenant there could be the covenant remnants AKA the Storm Faction which is much more focused on direct assault (more frigates and cruisers - less carriers), has some forerunner tech from requiem, and research geared towards weaponry, shields, planetary bombardment (and devoid of slipspace stabilizers!). which is to say- more in your face combat, less carriers and carrier squadrons, and less universal mobility for balance. or maybe just a "reformed covenant" faction utilising the same kind of gimmick the star trek armada mod uses for one faction that gives it the choice to decide what overall path it will take in culture and research. follow the arbiter and be more reserved, or Jul 'Mdama and be aggressive?
hell, even the forerunners could potentially have their own AI-led rebel faction! since their backstory is "a group of awakened forerunners dotdotdot" (right? i only briefly skimmed through the forum) there could be a rebelling AI faction. the halo: escalation "the next 72 hours" arc shows (slight spoiler alert) a sorta-kinda halo monitor (859 Static Carillon) make a deal with a certain angry forerunner, get completely guilty when seeing that whole situation unfold, and then help a certain color coded team of badasses kick ass on his former master. (plus lets face it, a faction inherently immune to the flood opens up some intresting possibilities...)
well that was a mouthful, but i'm not done yet (nows a good time to get coffee or popcorn)
ships:
for UNSC + any future derivatives:
Gorgon-class heavy destroyer (http://halo.wikia.co...heavy_destroyer http://halo.wikia.co...UNSC_destroyer)
the Gorgon could serve as a slower and cost inefficient but stronger defensively and offensively than the paris class frigate (it only has 1 MAC, and was the first to ever HAVE a MAC too!). the only real problem would be making a 3D model since there's not much to go on. however there may be panel in halo wars: Genesis where it is seen, and apparently it looks more primative than the Heart of Midlothian, AKA Halberd class. apparently Dr. Halsey references it in a book, probably fall of reach (oh just click the damn gorgon link already)
UNSC shield-generator ship (http://halo.wikia.co...Generator_Ship)
it's exactly what it sounds like. like a huragok, but it's a spaceship that project an AOE shield. it could also probably capture neutrals too if its description is anything to go by. perfect to take a bit of the edge off of UNSC ships sucking hard against their covie counterparts. but just a bit.
RCS-class armored cruiser (http://halo.wikia.co...armored_cruiser http://www.halopedia.org/RCS-class_armored_cruiser)
a much more defensive-minded counterpart to the CCS. it has less capital ship weapons but is more rugged with better armor and shields, better point defense, planetary bombardment, and has the ability to basically EMP a capital ship for a time. ...i'll take 1000 of 'em.
Covenant Supercruiser (http://halo.wikia.co...nt_supercruiser)
this is the bane of the Pillar of Autumn. and super MACs... and archer missiles... and Reach. ridiculously powerful shields (shrugged off a shiva like it was nothing), bisected a destroyer with it's ultra-long range plasma projector. and snipes orbital platforms as a hobby. replace the sniper that's already in SotP with this beast. who knows, maybe it will win its 1v1 with an Autumn class this time.
ORS-class heavy cruiser (http://www.halopedia...s_heavy_cruiser http://halo.wikia.com/wiki/Reverence-class_cruiser)
this is the ship that will make the CCS battlecruiser old news. and it would be a perfect fit for the aformentioned covenant derivative factions. almost twice the size of CCS, forerunner tech enhancements, more weapons, and a sweet ass new design straight out of 2015 (but apparently destined to first be seen and used in a board game?). this chance is just too damn good to pass up! plus hey, get this beast ingame and you can call firsties on it. seriously, if the autumn class is the enhancement of the halcyon, this is the supercharged version of the CCS. (as you can see, i'm fangasming right now) plus it might technically be the reverence class from ghosts of onyx?
Agricultural Support Ships (http://halo.wikia.co...al_Support_Ship)
it may stretch things a bit, but the ASS's (lol) could just be a mobile repair ship or even a specialied support ship to increas the expansion rate of growing populations of newly annexed planets for the covenant.
Keyship. in addition to presumably being part of the forerunner faction could possibly overlap with the covenant by being a potential covie titan? it would make sense seeing as there is only one and nothing could beat it. even when the pre-covenant Sangheili fought against the san 'Shyuum against it, they had to use forerunner technology to just battle it to a draw.
and lastly, structures.
the Unyeilding Hierophant. could it be a counterpart to the haven starbase? it could be a more specialized starbase focusing on repair and being a giant target with insane shields and squadron capacity.
the glassing cannon. thanks to halo: escalation, the covenant have a potential defensive option for their planets! it's exactly what it sounds like, plus it did almost destroy the UNSC infinity (spoiler alert BTW... oh hell i don't care it's just that awesome). it could be the covie answer to the super MAC, but cost more tac slots for balance.
yes... finally done! after 2 hours! wow i really did my homework this time.