Aquaman has become Warner Bros.' most successful DC movie since The Dark Knight Rises, so it's no surprise the studio wants to continue riding that particular cash boogie board for as long as audiences will let them. And that success (along with some legally-binding contracts) also guarantees that Jason Momoa, Amber Heard, and a few others will be riding it out with them.
As for director James Wan, Deadline reports that the Australian filmmaker would love to return to Atlantis for the sequel, but not until there's a script that he deems worthy. "Director waiting to make movie until there's a good script for it" isn't exactly surprising news, but there ya go.
In the meantime, Wan is said to be taking a "much-needed break" before directing another blockbuster. As Deadline notes, he's the only filmmaker who has made not one, but two blockbusters that have grossed over $1 billion at the worldwide box office for separate studios (the other being Universal's Furious 7) – so it would seem that he has more than enough leverage to do whatever the hell he wants next. And if whatever the hell he wants to do next involves, say, sticking a man-bunned Patrick Wilson on top of a giant haunted-as-shit seahorse with Vera Farmiga wielding a trident at his side, so be it.