Being down here in AZ for the last few years and watching Sam Keller, I can tell you that he would be a great bridge between Taylor and the next good quarterback at NU.
Keller's off-field problems are basically rumors like: He likes to party a lot, drink a little too much and have too much fun. If you've seen the co-eds at ASU, who could blame the kid. Also, he's kind of cocky and many of the ASU players didn't really like him off the field.
Also, other rumors have been circulating that when ASU coach Dirk Koetter named Keller his starter on Friday, Rudy Carpenter was very upset and was pondering his future at ASU (re: he was going to transfer). So, instead of losing a pretty good quarterback for three seasons (Carpenter's a sophomore), Koetter, after meeting with several players who wanted Carpenter to be the starter because they liked him more personally, Koetter decided he'd rather lose a pretty good quarterback with one year left.
If Keller transfers, ASU has nothing behind Carpenter, but if he can make it through this season without getting hurt, Koetter can recruit a guy to groom.