College is not for everyone and it is important first and for most that the student be committed. a student who does not wish to learn will not get anywhere no matter what the incentive. But if the student is committed to doing the work, three years is a perfectly reasonable amount of time.
It's a heavy workload, no question, but one that can be handled and some people already do it. If there's one way to get the attention of college students it's to offer them financial incentives, I think you would see a lot of three year graduates if they have a monetary reason to be them.
I think that there are some college students who can finish their education in three years if there were some financial incentives offered for them to do so. I do not think it's only a matter of money though. I think a lot of people just cannot simply try to go to school for that many hours a week.
As a student who attempted 18 credit hours in one semester a few times I have to disagree, students would not be able to finish in three years, if financial incentives were offered. The problem with this is in the scheduling at the colleges I have experience with. I've attending a community college, a private college, and a university. At each school I experienced schedule problems that dealt with the school not offering enough required classes for students to take them when they really needed them. This ended up making my required classes extend over the four years and it also ended making my expenses so high that I could no longer afford to finish my degree. Financial incentives to students will not fix the problems within the colleges.
If they could just concentrate on schooling as their full-time job and not have to worry about finances, they could probably finish school in even less than 3 years. Perhaps even two. I did an accelerated course for my degree and finished in a mere 18 months. So yes, of course.