Many people will not go for this. Sure, it's enticing for everyone when they see the payout. However once they look at the entry list and determine that they have no shot at the prize due to the caliber of drivers entering then they won't want to 'waist' there money for the same amount of runtime they may normally get just to give more money to the eventual winners.
The closest thing done thusfar was the NitroCross world Championships.
They had an invite class that raced for all the money. Most of the money was brought in through outside advertisers and corporate sponsors. It was a 25k purse with 5k going to the winners of both pro buggy and truggy. They paid out the top 10 in Invite I believe. This event however didn't have totally outrageous entry fees and still had expert and sportsman classes with many prizes I believe.