I've seen fan-art of an Ezra/Leia non-romantic pairing in various places on the 'net, so having a short arc (two episodes) with Leia as a guest character could be interesting.
She's about Ezra's age, and it might help further develop the Ezra/Sabine dynamic if Ezra is able to interact with a girl his own age, and maybe help (most likely unintentionally) give Ezra some clues on how to actually talk to Sabine and get her to actually like him as opposed to the unpolished cheesy attempts at "smooth" talking that he's tried in the past.
Han Solo might be interesting, though unless Kanan and Ezra play it real close to the vest regarding their Jedi-ness, don't quite see how Han's dismissive attitude about Jedi and the Force would hold up after seeing a couple of them in actual action.