Are you OK with a state reducing its voting age to say 16 or even 12 to boost the raw number of votes cast?

If after 95% of the votes were in it was found that the candidate with 60% of the vote had hired a hit man to rub out the spouse, then are you stuck with this loser?

Do you require a majority or will a simple plurality do?  If only a plurality, are you OK with an outcome where the candidate with 12% of the vote wins in a ten candidate field.

If a state adopts "acceptance voting" (where you can vote for as many candidates as you like) would that be a problem?  Some see acceptance voting as a way to keep Nader type candidates from screwing up tight elections.  

Would you be OK with discovered ballot boxes long after the vote in Chicago that tipped the election to the mayor's favorite?

A simpler solution is to simply require winner take all primaries.  The proportional system as this election proves is prone to not producing a clear winner.