Ahsoka Tano should appear in the Disney+ series Star Wars: Ahsoka, also in production, Ahsoka could easily appear in the Andor series before her own.
Cassian Andor has been a soldier since he was a child, during the Clone Wars. At six years old, he was part of the villainous Separatist Alliance and saw combat by way of throwing debris at Republic Clone Troopers. The full story of how Cassian ed the Rebellion is unknown, but according to Rogue One: The Ultimate Visual Guide, he was brought into the fold by Davits Draven. Cassian’s reprogramming and subsequent recruitment of K-2SO were portrayed in Marvel’s Rogue One - Cassian & K-2SO comic, but other than that, most of Cassian’s Rebellion-era adventures before the events of Rogue One are currently unknown. Because of this, there is plenty of potential for adventures and character development in Andor.
The Mandalorian. Ahsoka was also a reoccurring character in Star Wars Rebels, working with Bail Organa and Hera Syndulla throughout season 1 as a mysterious Rebel agent known as “Fulcrum.” After her true identity was revealed, Tano became a reoccurring character throughout season 2, until her presumed demise at the hands of Darth Vader on Malachor. In truth, she was saved by Ezra Bridger via the “World Between Worlds.”
5 BBY, the timeframe of Star Wars Andor, is concurrent with the first seven episodes of Star Wars Rebels. Ahsoka was very active in Bail Organa’s Rebel network at this time, appearing in a voice-only role as Fulcrum in the Star Wars Rebels episode "Out of Darkness." Ahsoka’s Fulcrum moniker is used by several Rebel spies, such as the Imperial ISB Agent Kallus (who defects to the Rebellion in Rebels, season 3) and Cassian Andor himself. With both Cassian and Ahsoka having used the Fulcrum codename and both being active in 5 BBY, the two may work together, with Ahsoka possibly training Cassian as a Rebel spy.
Cassian’s own past as a child soldier for the Separatist Alliance may come into play as well. Although General Draven is said to have recruited him, Ahsoka may have also taken part in Cassian’s transition from Separatist to Rebel. This could be a source of conflict between the two, as Ahsoka was once a Republic Jedi (and is particularly fond of Clone Troopers), but Ahsoka is also demonstrably willing to find common ground with Separatists, as seen in the Clone Wars episode "Heroes on Both Sides," where she befriended Separatist Lux Bonteri. In addition to Ahsoka potentially taking part in Cassian’s recruitment and training as a fellow Fulcrum agent in Star Wars Andor, she may also task him with recruiting other former Separatists to the Rebel cause.