The Disney Parks Blog announced a new date-based ticketing option that will debut October 16, 2018. This new ticketing will result in seasonal pricing for multi day tickets and lock guests into specific dates where their tickets are eligible. An additional "Flexible" ticket option will also be available for an additional fee. The video below explains the system and establishes a price point of $100 for the flexible ticket option.
As part of this change, all four parks will one again be priced at the same level for single day and multiple day tickets. New single day pricing is expected to increase to $109-$129 depending on the season.
This was first rumored by Len Testa on August 8th on Twitter.