The Syracuse joke is relevant because if you start Book now, he'll be going against NFL caliber LBs, DBs, D-Lineman and coaches. 90% of the guys he went up against in college will never sniff a NFL practice squad.
That said, what do you get / lose by putting him out there, behind a beat up O-Line & a receiving core that has a hard time catching balls that hit them in their hands? What will coaches be able to evaluate that they aren't already able to see from him in practice against our guys on D? What kind of experience is he going to get from a meaningless exhibition game that he's not getting in practice?
If you are high on his upside, and you're trying to keep him under wraps...I think you just finish out the season with Hill and see how the competition goes in the offseason.