Appointing Ensign Tilly over several lieutenants creates a rank problem while Commander Burnham remains aboard. One possible explanation is that Tilly would accept Burnham continuing to do the executive officer's work, whereas a lieutenant would expect to perform the job. Another is that Burnham could receive a separate command. Tilly's appointment could also be an opportunity to develop a character given less attention than Burnham, although none of these explanations is settled.
Notable Point · 2:06:13-2:07:31
How can Ensign Tilly serve as executive officer?
Tilly's appointment raises questions about rank, Burnham's continuing role, and whether the story is preparing a larger role for either character.