Credits information reveals Misty and Brock in March 7 anime episode
A cast list for the upcoming anime episode BW116 on March 7 includes the Japanese voice actors for Brock and Misty in those roles. In addition, a poster for the sixteenth movie has surfaced, which includes Sableye among Ash and his friends' Pokémon.
Due to the lack of promotion of their appearance and the reappearance of Ash's Charizard in BW116, it is currently expected that Misty and Brock will only appear in flashbacks.
Note that readers may need to change their character encoding to properly view the cast list; Japanese (Shift_JIS) is the necessary encoding.