There are also things like Qimir's backstory, which is unlikely to fit into the last episode. It's possible they will be addressed in tie-in media rather than on TV though. Too much backstory kills plot momentum.
Now, there is also the exact nature of the witches. We had one comment with respect to that: "Nightsisters?", left as a hanging question. The vanishing in a puff of smoke trick (illusion?) is something Nightsisters have been depicted doing (The Clone Wars, Fallen Order). They also like a bit of archery. However, Ahsoka revealed the Nightsisters did not originate in this galaxy, and did not originate on Dathomir. The next new Star Wars show is Skeleton Crew, which is advertised as revolving around a ship lost in another galaxy. I would hypothesise that is the same galaxy Ahsoka is stranded in, and the one the Nightsisters came from. Therefore we might learn more about witches in that story.