The answer: it won't. It wasn't a huge upset, and is certainly not among the greatest upsets in college football history. Anybody with any knowledge of North Dakota State's program could have reasonably expected this outcome to occur.
The NDSU Bison are an FCS powerhouse. The program has won five (!) FCS championships in a row. From the beginning of the 2011 season going into Saturday's game, the Bison were 73-5. During that time they've defeated FBS schools Kansas State, Iowa State, Colorado State and Minnesota.
As I wrote in my 2007 post, what I consider to be the "biggest upsets" in college football are those
...which occur when one program is so thoroughly outclassed and so overwhelmingly outmatched by another in terms of stature, resources, and/or athletic potential that it shouldn't have a snowball's chance in Hades of winning, yet actually pulls it off.This simply does not apply to North Dakota State. They might nominally be an FCS program, but they are so talented and well-coached that they could beat just about any FBS program; "outclassed" and "outmatched" they most certainly are not. As USA Today's Dan Wolken notes, NDSU's defeat of Iowa doesn't seem like an upset because "it’s just what North Dakota State does."
On a related note, FCS upsets of ranked FBS teams, while still a rarity, are no longer unheard of. Since Appalachian State's upset of Michigan in 2007, we've seen James Madison knock off #13 Virginia Tech 21-16 in 2010 and Eastern Washington beat #25 Oregon State 49-45 in 2013. (And don't even get me started on FCS victories over unranked FBS teams, which happen pretty frequently: there were three of them - all against teams from so-called "Power Five" conferences - on the first Saturday of this season alone.)
FCS victories over FBS programs are noteworthy, due to the advantages the FBS schools typically have over FCS schools in terms of fan support, facilities and scholarships. But they do happen, because Any Given Saturday. Moreover, North Dakota State is not a typical FCS program. They are as dominant a program as there is in any level of college football right now, and their victory over the Iowa Hawkeyes, while admirable, is simply not extraordinary.
See here and here for my previous thoughts on the subject of FCS teams defeating FBS schools.
(*Since I wrote my post in 2007, other top ten college football upset lists have been created. Check out these slideshows from bleacherreport.com and fansided.com.)