I'm kind of expecting an Arbiterless Halo 4, then a surprise appearance at the somber close of a Halo 5 chok full o' human ass whoopins, then a "unite the galaxy against the common enemy" type deal in H6 (spearheaded by the Arbiter with his relatively close ties to humanity ((meaning the majority of Sangheili would be on board, the rest are presumably the backbone and leadership of the reformed Covenant, replacing the Jiralhanae* and the San'Shyuum*, respectively (the other species of the Covenant and the remaining Brutes* and Prophets* would likely be conscripted somehow as well (probably the impending doom bit :P))); he'd be all "yo, we're all gonna die unless we work together to defeat this ancient foe, you guys, we must unite as brothers! Hnuah!"). I really, really love the Arbiter (and good ol' (green-eyed) Rtas for that matter) as a character, and would just be ecstatic if he were to return for this new trilogy. The possibilities, in the hands of good writers, are endless. Plus, Keith David's voice, I've heard, is extremely good for your health.
Long winded as fyuck lol :)
[Edited on 07.12.2012 9:40 PM PDT]