This one may be a tricky, seeing as, technically speaking, Supergirl and Powergirl are different versions of the same character. But, since its been confirmed that the show is connected to the Arrowverses multiverse, meaning that alternate Earths are now fair game, and Powergirl can join the show. In the comics, what differentiates Supergirl and Powergirl is age. Powergirl is the Supergirl who grew up and shed the iconic S in order to establish herself as completely independent from her cousin. This idea could make for a great episode, or even a great mini arc. For example, what if on Powergirl's Earth, the pod that brought her to Earth was never knocked off course, and thus Kara was found by the Kents alongside Clark? This would mean that in this universe, Kara would become a superhero first, and not have to crawl her way out from under her legendary cousin's shadow. It would be interesting change of dynamic, seeing as Kara was originally meant to be Kal-Els guardian and protector, not the other way around. In this world, Kara Danvers would be Kara Kent, and would have far different relationships with the entirety of the cast. She and Alex wouldn't be sisters, and may not even know each other. She'd have grown up in the Kansas countryside, raised by farm folk instead of by scientists, resulting perhaps in an accent change or even a different personality. The entire dynamic of the story would be different, and it would be cool to see Kara react to how her life may have ended up. On top of that, it would be amazing to see Melissa Benoist take a shot at playing a Kara tempered by a dozen years more experience.
