As I see it based upon the 3 that I've seen throw, here's what each would need to do to win the starting spot:
Trent McKinney; really needs to show improvement reading through his passing options and his throwing. When I say throwing I'm thinking on two points, medium/longer passing and ball placement in shorter throws. McKinney seemed (at times) to rush things and would throw some knuckle-ball type passes that the WRs were having a hard time pulling in.
Shay Smithwick-Hann; Continued progression in the zone-read, sure he ran it in high school but at this level he doesn't really deceive/fool a lot of defenders. Needs more zip on his pass, throwing arcing rainbow passes 50 yards down field only works a few times per game.
Gerald Kemp; Biggest issue is the short passing game, Kemp can go into Roper-mode and start throwing off his back foot. He over-throws a lot in the short game and his placement of passes is hit and miss. Not sure if it's fair to point it out but durability is a concern as Kemp was banged up for a lot of the 2011 season and then carried it forward with a new injury 1/2 way thru spring ball.
On the other hand, here's what I see each could bring
Trent McKinney; the spring game showed he's got wheels and can run the spread-option well. His biggest foe on the field was himself as he had two long runs where he slipped and fell or else he'd still be running, lol. Trent has a quick release and when he's not forcing throws he operates the hurry up "Fuji" offense pretty well. In terms of IF this team now goes big time run-heavy, might as well have Trent get out there and run that offense. Probably keep his number of passes under 15 - 20 per game.
Shay Smithwick-Hann; Shay is the best passer overall that I've seen. He hits WRs/RBs/TEs in stride on short/quick routes pretty well. Saying he can't run is too blunt of a statement, he has some quick moves and ran the spread offense in HS - so it's not like he's a pocket QB trying to learn the spread system. Shay is also in his 3rd year now on the team, he's familiar with all of his WRs and has to be an emerging team leader. Shay could run this offense like a 2007 Cole Bergquist did - coming into his own, throwing for 220ish per game, less than 30 attempts per game, and running for a 200-300 yards on the season. But obviously relying on the RBs to do the majority of scoring and big playmaking.
Gerald Kemp; This could be Kemp's break, I'm not sure where he stands with the team when he reports but considering the log jam at WR and the need to get the best QB now that JJ is gone - Gerald might just be that guy. Kemp was ahead of SSH and McKinney entering spring ball. We all know he's a tremendous athlete, a fast runner, and pretty good in the zone read. As a senior he could emerge into an on-field leader and hopefully the summer suspension (and hopeful re-instatement) has given him a wakeup and helped his outlook. Also, I still go back to the UNC game, Kemp played pretty darn well in that game, probably some of the best I've seen him play which leads me to think he might be a gamer that sometimes isn't "up" in practice but knows exactly what to do come gametime. Houston Roots was kind of that way last year, he was solid but not great in practice, come game day though he really was the 2nd best playing corner in the Big Sky last year.