This is probably irrelivant, but I thought I may as well post it. Looking through the hiring list on the 343 hiring website, there is a job for a cinematic animator:
link
It probably just means regular cutscenes, but it made me wonder anyway. If Master Chief turns out to be non-customisable, I wouldn't see a problem with cinematics like in Halo Wars rather than using the game's engine, such as in the other Halos.
What do you think?