If it was last year, or if he was still at OSU, he could be a darkhorse candidate. His USC ties, respect among the coaching fraternity, and obvious challenges with winning at OSU might be able to overcome the age factor and mediocre-record factor at OSU. I doubt he would have gotten the job, but his name could have been thrown about for serious consideration and may have been contacted or even interviewed.
But timing is everything, and the timing is poor. At the moment, it's hard for anyone not to notice that we are currently 2-4 after seven straight seasons of 9-4 or 10-4. And big contributing factors to those losses have been clock management and penalties, which happen to be areas where coaching is supposed to have more of an effect than talent. That is really undermining the "it's hard to win at OSU" excuse for his overall winning percentage right now.
Our team could turn the corner and begin winning now, and Riley may look more like the coach many hoped for by the time USC hires their replacement in December or January. Big IFs, and still not enough for USC in my opinion.
USC fans want a sexy hire, and Riley isn't it. He might have been back in 2008 or so, but not in 2015.