It is possible if not probable that a team will need their backup QB to play some meaningful time during the course of a season and potentially start a game or two. That being said, I think we saw the benefit of having a guy that changes the way a team has to gameplan for your offense when we saw Troy Smith start those games for a desperate Coach Singletary two years ago. He was a completely different animal than Alex Smith was and teams were hesitant in their defensive gameplan and it allowed for some initial (albeit short-lived) success for Troy and the team.
In the event that Alex goes down for a couple games this season, they may be looking for a change of pace guy like Kaepernick to come in and play the wild card for the couple of teams they face. You can alter an offensive game plan dramatically for a couple games and squeak out a couple wins. If they had to deal with losing Smith for a whole season, I think you may see more attention paid to a guy like Tolzien who plays more that style of football and would maintain consistency with the offense.
My bet is Kaep gets the backup nod for publicity purposes and Tolzien beats out Johnson for the 3rd spot. But if they actually are forced into action, the situation will dictate who gets the starting role.
[ Edited by jesserdumas2 on Aug 14, 2012 at 5:59 PM ]