Not everything sells out right away, though. I've bought concert tickets on the day of the show more than once. Somehow they still managed to have all the concessions staffed.

But regardless, the formula for decreasing the price could be adjusted. For example, it could be an exponential decay toward the reserve price, with the decay rate set so that most of the decline in price is early.

Or, for shows that are entirely general admission, like festivals, you could use the alternative form of dutch auction: when tickets go on sale, everyone bids what they're willing to pay for some number of tickets. Then the bidding closes (with ample time for planning), and the bids are cleared in descending order of price, and everyone pays the amount of the lowest clearing bid. This method would find a price closer to the true market price of a ticket and discourage speculators.

The issue is that most events don't even sell out. This is a terrible idea.