Cute, but the whole series would need to build up and work towards that instead of adding it last minute. They'd needed to have made a book four or restructure the series beforehand.
There's some potential though. She could have been separated and stranded with Aang in the same way as Zuko and Kitara, where they bonded a bit. Develop a friendship, the seeds of a relationship later on. She still wants to and feels obligated to serve her father and become the Firelord, and takes that throne in the final season, forcefully breaking off her ties to the Avatar due to knowing Aang will likely die against Ozai. Zuko and her fight, she cheats against the two to gain an advantage, but then Kitara challenges her emotionally by making her realize Aang is going to die because of her, not Ozai. Her will is weakened enough for the two to put her down, and later she willingly gives up the throne to Zuko so she can live with Aang.
It'd be cringe if it were just done in the last arc, but if it were built up for a while it could be great, and satisfy Zuko-Kitara shippers at the same time.