Ok, - Based on what I've been gathering - I'm 99.9% Sure that the Acolyte will be the Mother Talzin Origin Story and will heavily involve the Night Sisters and a Young Darth Maul, Young Ventress, etc. The Mother Talzin rumors have been circulating for some time however nothing substantial has been confirmed of course.

Acolyte = Sith Apprentice

From Mother Talzin's BIO on Wookiepedia

Talzin's expertise in magicks was significant enough to attract the attention of the Dark Lord of the Sith, Darth Sidious, who came to Dathomir ostensibly to trade dark side Force teachings with Talzin and take her as his own Sith apprentice - instead, the Sith Lord abducted Talzin's son Maul and took him as an apprentice in her place.

With the show focusing on the Nightsisters - Leslye can delve into the intricacies of lesbian relationships when showcasing the strong bond and Sisterhood of the Nightsisters sect.

This could be an extremely interesting story. Showing Talzin training as Sidious's apprentice, seeing a young Darth Maul, and of course a young Asaj Ventress. After being spurned by Darth Sidious we could see Talzin delve deeper into dark magic and witchcraft in her quest to exact revenge on those who have wronged her. Dathomir is also a very creepy and intriguing place, plus, one of the best story arcs in the Clone Wars was the Son's of Dathomir. This will also allow us to see our favorite Starwars beast the Rancor since they're native to the Planet.

There are so many things they could do with this character, location, time, and place that the possibilities are endless. Until we get something more concrete for Lucasfilm as to what the show will actually be about this would be a very fun period in terms of theory crafting on what this show will be about.