Currently, the Carnival Splendor is scheduled to have a maiden voyage from Sydney in December 2019. According to Carnival's press release this will follow a repositioning cruise from Singapore.
Prior to its new deployment from Sydney, the Carnival Splendor will undergo a major dry-dock that will involve adding a new waterpark as well as features geared towards Australian cruisers. No additional details about this dry-dock were available at the time of writing.
The Carnival Spirit's new homeport has not yet been announced, but Carnival will probably make an announcement soon.
If you would like to read Carnival's press release: Click Here - this link will take you away from RyG's Cruise Guide