I have a friend who graduated in 3 years and he was a TKE. Because his father had passed away, he was only eligible for Social Security payments if he started college full time before he was 18. Therefore, he had a full course load at the community college during his senior year of high school. With one semester already under his belt, a few extra credits each term and some Spring/Summer courses, he finished in 3 years. I could see this happening more as more students graduate from high school with a semester of college credits already under their belts due to AP courses/exams.
Personally, I think college was the best 4 years of my life and there's no real reason to rush to adulthood
I don't want my kids taking too long either though, due to finances. 4-4 1/2 years seems reasonable to me.