I've liked him for every DC search here since Diaz left the first time.
That said, his D at Florida this year was bad. Granted the offense didn't help, but still. This year was his first time calling a defense since sometime between 2006(his last previous DC gig) and 2010(his final season as HC at Miami). Recency bias and how quickly new offensive wrinkles seem to weed out old school DCs that can't adapt makes me nervous about Shannon. I've yet to see proof that he can adapt.
ETA: at first glance I'd be fine with Moorhead bringing Brent Pry with him. Bob Shoop sure seemed elite as long as he was with Pry at Vandy and Penn St then crashed and burned by himself at Tennessee. Pry had a top 15 D this year after a top 40ish D in his first year as a playcaller.