Has their been any story threads that suggest that the Didact wasn't the only Forerunner still alive?
Additionally, has their been any mention to the Composer leading for the digitized to life, rather than the other way around?
Guilty Spark #2 is convinced that the Librarian is still "alive".
The Librarian mentions that their attempts to return composed individuals "to biological states created only abominations" (foreshadowing for Flood 3.0?)
"He would have encrypted your entire race"
As in disintegrating them?
"I would have glassed your entire planet!"
"One single Flood spore can destroy a species"
"The rings will kill us all."
You know, focusing on the story of Cortana would have been the perfect opportunity to maybe lower (or rather "shrink") the galactic stakes a bit, while raising personal ones.
Humanity barely survived the original trilogy, every other race is in turmoil, but instead of toning it down a little, maybe showing how an actual in-universe society operates for the first time, instead of showing the challenges of rebuilding after everyone's civilizations, cultures have been destroyed, we get humanity at its most badass since... uh... prehistory, as close to ruling the galaxy as we've ever been, reigniting the original conflict for amusement. So, clearly, we're going to need an enemy to match our newfound power, even if he has only one ship (and some spacefaring sidekicks, but those don't really matter when we can just fly through them).
Meanwhile, you as a player will mostly run around pushing buttons. A thousand lifetimes orchestrated to create a mass killing button pusher, now important only because the plot places him in the right/wrong place at the right/wrong time.
It might be just me, but the balance between the players', their character's and his world's stories seems completely messed up, more than ever.