Stolen from reddit:
Key points from the Live Letter

Patch 4.5

Part one release date: Jan 8th 2019

Part two release date: Late March 2019

Trailer: https://www.youtube.com/watch?v=MJ4zjFWLnAA

Patch 4.5 Part one

Blue Mage will be added on January 15th, one week after 4.5 part one arrives

Gold Saucer: Doman Mahjong, Air Force One GATE

Patch 4.55

Eureka: Hydatos

Rival Wings: The Hidden Gorge

Patch 4.56

Hildibrand

Patch 4.57

World Visit system

Patch 4.58

NA & EU datacenter changes and new worlds.