Eh, I don't know, MC really can't be partnered with anyone who doesn't measure up to his impressiveness. Anything less than the Chief will just feel like a side kick. And the Chief definitely doesn't use side kicks.

: The Forerunner trilogy has also introduced the possibility of geas, so maybe
: whichever one was unlocked with the Chief's gene song could do the job.
: Also wasn't he hearing the Didact in his head by the end of Halo 4?

Now that actually might work. It would be hard to convey it as a legitimate development to those who haven't read the books. It would just seem like "Oh Forerunner magic put a voive in the Chief's head. Wonderful."

And on the topic of Forerunner magic, I hope they give a little more detail about that gene song of the Chief's. Having read the books, I understand it, but it was presented in a very smoke and mirrors way in the game.