This is a thought experiment.
According to the US Department of Education (reported in wikipedia), the University of Minnesota has (Fall 2013) 63,929 students, ranking 19th in the US. Of course, many of those larger schools are for-profit, non-residential, cater to part-time students, or college systems. Among “peers”, (land-grantish research schools) larger schools include Arizona State, Central Florida, Ohio State, and Maryland.
Alternatively, the Twin Cities campus is the 9th largest public university in the US by enrollment, with 48,308 students (undergraduate about 34,500), falling several places, and several thousand students from 2009, when it was 4th.
But US universities are pikers compared to some others in the world. The National Autonomous University of Mexico has over 324,000 students. The University of Paris has XIII parts, which collectively have about 330,000 students.
There are numerous economies of scale to be had from a larger school (i.e. costs rise sub-linearly with the number of students because the delivery of education has a large fixed cost component like buildings and chairs and lectures and software and administration), and the evidence about quality of education with size of school (and even to an extent size of classes) is mixed (though everyone seems to like smaller classes better). (The evidence about student satisfaction tends to favor small elite liberal arts schools with a lot of hand-holding, land grants like the University of Minnesota will never compete in that market). These economies of scale should lower per pupil costs. Rankings like US News favor small class sizes, but also favor large universities.
Clearly the University of Minnesota rejects more students than it accepts (it has a 44% acceptance rate). If it just one year raised that to 88% several things would happen. First there would be more students (though it is not clear enrollees would double, more than double, or less than double, since rejected students might be more or less likely). Second, because it lost some of its exclusivity, fewer top tier students would apply. Many faculty would similarly find alternatives – not wanting to deal with the headaches twice as many students brings, though I imagine teaching slots would be filled with the glut of PhDs on the market in most fields. Class sizes would undoubtedly increase, but more classes could be offered. [After World War II, Georgia Tech, which saw an influx of GIs, expanded its night school, so that there would be a full second shift of courses]. Yet the quality of the University would on average drop.
Trends working in the opposite direction of increasing campus size include MOOCs, encouraging more online, distance learning. Getting those to work well has been difficult, and they are yet to be mainstream. Moreover a seldom-stated purpose of university, keeping students out of the labor market and in a semi-protected environment between home and the harsh cruel world cannot be accommodated with MOOCs. Demographics also move against rapidly expanding university size overall. However any one university should be able to increase market share, both with domestic and international students. Another purpose of university, providing a mixing bowl for organization of individuals into groups and couples, requires in-person attendance.
However if this were done more gradually but intentionally, with an aim of attracting more and better students, it should be possible to grow the campus to 100,000 over a decade or two.
From a physical perspective, the campus has significant room to grow, especially to the North East, but also infill and intensification to the south-east, north, and on West Bank. Even more growth is possible on the St. Paul campus, which abuts the largely underutilized State Fair Grounds.
My guess is doubling enrollment would require far less then twice as much new classroom space, about a doubling of dorm and residential space, a bit less than doubling of graduate student offices and labs and faculty offices – less assuming many of the new teaching responsibilities would be borne by adjuncts rather than regular faculty.
Around campus, business would boom. New apartments, with ground floor retail and restaurants would fill in any of the empty parcels of Stadium Village and Dinkytown and West Bank.
Transit ridership to campus would more than double, since the capacity for cars on campus would decrease significantly (all those new buildings will use up surface parking lots, reason itself to support an expansion, pedagogy be damned) while total travel demand in terms of trips to campus rose.
Such a change would challenge Boston’s 250,000 students (not sure how this was calculated, must be “Greater Boston”) as the lead college town in the US. According to city-data, Boston’s college population is 14.6% of the total. The City of Minneapolis has 11.3%, near the top for large cities. Increasing enrollment by 50k students would increase the share of the City’s population in college by up to 12% (depending on where they lived, the maximum assumes they all live in Minneapolis proper), putting Minneapolis at about 23%. Clearly much of Boston’s attractiveness to college students is the surfeit of students already there. We don’t really operate in that league here yet.
If we think of college as a temporal port, just as immigrants from Europe used to land mostly in New York, and occasionally disperse from there, immigrants from youth land in college, and disperse slowly from that point. This should greatly increase innovation, as the region’s engine of growth scaled up and the region attracted boatloads of Generation Z/Post-Millennials to its lake shores.