rewrite is still underway, according to Chris Priestly:
Also, if anyone is interested, Jessica Merizan, Chris Priestly, and Fernando Melo held a reddit AMAA
I'm as critical of Bioware and ME3 as anyone, but I actually think she got it about right when it came to Harbinger. His role in the story is right there in the name.
Harbinger. A herald. To foreshadow a future event. To make known the approach of another.
I wouldn't have objected if he'd had a role in ME3, but I didn't miss him, either.