As of today, eighth place in Iowa would most likely belong to Mike Huckabee, Rand Paul or Bobby Jindal, all of whom have been mentioned as serious presidential contenders at some point in the past. Huckabee even won Iowa in 2008.
This is still true. To return to our horse race analogy, this field is not strong because it features a Secretariat, a Man-o-War, a Seattle Slew, and a War Admiral. That would be more akin to the 1988 Republican field, which featured a sitting vice president to a popular president, a former vice presidential candidate and sitting Senate minority leader, and the godfather of supply-side economics with a devoted ideological following. That field was strong because it was so top heavy, though it was not particularly deep. The strength of the 2016 field lies in the fact that, although there are no Secretariats, there are an unusually high number of potentially derby-ready horses running.
Two relevant points follow from this. For starters, without a Secretariat, there is no one who can automatically squelch insurgent campaigns. To be more direct, no one can do this cycle what George H.W. Bush was able to do to Pat Robertson after Robertson finished ahead of Bush in Iowa. These insurgencies will linger, especially since Donald Trump, with years of communicating to average Americans through his television show, is stronger than many of the previous insurgents.
In addition, with everyone so tightly bunched, there is little incentive not to stick around, if a candidate can stomach carrying his own bags, a la McCain in 2007.