The planet where it all started really should make an appearance in the movie where it all will end. Tatooine is a desert wasteland that is sparsely populated but was the home to two of the most powerful beings in the entire universe.
How this backwater planet will be incorporated is the question. If Rey is out to collect Jedi artifacts, which seems to be the case, searching Ben Kenobi’s home on Tatooine would be a logical place to look. He had a lightsaber just sitting in his living room trunk so the chances are high he’d have another valuable Jedi artifact on his shelf or in a cabinet.
Another way in which Tatooine could be incorporated into Episode IX would be in a Ben Solo redemption arc.
Maybe Ben comes back to the light by the end of the film. He could feel guilty for his crimes, especially murdering his father and decide to exile himself. What better place to do that than Tatooine?
He could put himself in self-exile just like his namesake, and live out the rest of his days as a desert hermit. It would put the story full circle and arguably be a better ending than him just dying in the end at the hands of Rey or Palpatine.