I tend to agree with this and with @Mdot21 's analysis above but coaches in general and Harbaugh specifically tend to be conservative by nature so I have my doubts as to whether or not they'll actually do it.
One factor that may tip the balance in favor of switching to the new kid is that Michigan's OOC is ridiculously weak then their first league game is at home against Maryland. Thus, the Wolverines would have no excuse not to make it to 4-0 even without playing ANY of last year's starters. Thus, they have plenty of time to work on development before their first serious challenge (@ Iowa on October 1).
Conversely, this actually might lead to them NOT switching because the weak opposition could mask any weaknesses.
I admit, I try to look at it a little more like a coach, and thus I'll give the cop out answer.
Whoever can run the offense better should start. Simple as that.
Now, Michigan has a few months before it needs to answer that. It'll have player run practices, actual practices, plenty of film room and such. Can run that competition all the way up to the end.
Fact is, that's the position that is the least tools reliant. If the young kid is all that, he'll show he can run the offense, know where the ball needs to go, etc. And if he can make all that go smooth, he should start.
The sport is littered with guys who got handed the job because a coach needed upside or the backup wasn't working. And you learn that often, just because a guy is young, has tools and gets reps, it won't shoot him along the developmental curve. Sometimes it takes time. Sometimes, it's not there at all.
Which is all to say, you don't give it to him. You know what the older guy can do. Younger guy just has to go earn it by running that offense better.