Is that a definite thing? DL says it still exists for existing tickets:
"Unused non-promotional single day tickets that expire on December 30, 2020 or March 31, 2021 will have the expiration date extended to December 16, 2021. Wholly unused, non-promotional multi-day tickets that expire on January 12, 2021 or April 13, 2021 will have the expiration date extended to December 16, 2021, and the
ticket will expire 13 days after first use or on December 16, 2021, whichever occurs first."
From the new ticket page:
https://disneyland.disney.go.com/experience-updates/parks-tickets/