Yeah, I realized my mistake too late there.

: The benefit (coming from someone blithely ignorant of how computer graphics
: work) is that the models and art assets don't age. Instead of wasting time
: remodeling the assault rifle for every installment, 343i can just port it
: into the new game and focus on developing new content.

It'd be more of a re-skinning if anything.
But with each new hardware advancement, code does need to checked and sometimes adjusted to ensure it plays as well as before.

: Someone, please, tell me why this idea won't work.

I, myself, don't see any reason why it wouldn't work.