The late application closing date is due to Grant Bowler working on the new Syfy series Defiance, he has been cast as the main character Jeb Bolan, the central figure and focus of the series essentially.
Filming began on this in April, but it can take many months to make a tv show, I heard it'l be 13 episodes?
Depending on how successful the show is, and if it gets picked up for more episodes if Season 2 occurs, could mean that Grant will have to either work The Amazing Race into his schedule after filming each season(More likely), or someone else being brought in to replace him as Host.
I don't think this will have a major effect on Season 3, but could on Season 4 onwards if it occurs. Grant will be free to do the Season in the near future.