An overlooked detail in THR's report that Will Beall has been hired to write the script for Aquaman is the fact that director James Wan and the co-chair of DC Films have already written a treatment. As opposed to an outline, a treatment is typically 40 pgs long (on average), with very specific details regarding the story. This is a particularly important detail as the film currently has a July 27,2018 release date, meaning filming on Jason Momoa's standalone DCEU film needs to commence shortly thereafter Justice League wraps in London. With a treatment already completed Beall should be able to flesh out dialogue and scene transitions in relative short order with the tone and broader plot points already established by Wan and Johns.
From what we've seen of the trailer, DC fans should expect a badass Arthur Curry reminiscent of his depiction in Bruce Timm's Justice League and Justice League Unlimited. To date, the cast includes Momoa, Amber Heard as Mera and Willem Dafoe as Vulko.