I posted my own rough ODST 2 plot idea a bit ago if anyone cares to read it-
How bout it takes place after the halo events and its about a new odst squad consisting of Buck and Dare's kid whos the squad leader, Dutch and Gretchen's kids (fratenal twins), Romeo's cousin, and the Rookie's little brother who you play as, storyline could be about going after the remaining covenant forces, lost without their prophets, but still deadly and not too shabby in number, still doing guerilla attacks on the outer colonies. You and your squad could drop onto one of the remaining covenant ships and fight your way through the corridors to get to the bridge where you track the ship back to its orgins which leads to an unknown planet where you and the team drop in, but shortly lose connection with the rest of the human forces and while doing recon find out there's a massive covenant force there working on a high tech doomsday device to blow up earth, while sneaking around the base your team finds a holding cell with the arbiter in it, he came to the planet because of rumors of a regrouping of the covenant, you free him and he joins your squad and together, you ignite the doomsday device to explode the covenant planet, and make an escape