The Force Priestesses who first appear in Force Ghosts, maintaining consciousness after death through the Force. Obi-Wan Kenobi provides an opportunity to show the titular Jedi following in his masters' footsteps in a move that would profoundly affect his story leading up to A New Hope.
In Star Wars: The Clone Wars, the Force Priestesses are five mysterious Force entities that reside on the Wellspring of Life - otherwise known as The Force Planet and the source of the midi-chlorians. They represent the connection between the Living Force, which is present in all life forms, and the Cosmic Force, the timeless, spiritual side of the Force which the Living Force feeds when a living being dies and becomes one with the Cosmic Force. The Force Priestesses teach Qui-Gon Jinn how to live as a force spirit after death, something unheard of until then; Qui-Gon Jinn's Force Ghost spirit then directs Master Yoda to them to learn the same secret. They put Yoda through a series of trials, in which he encounters the personification of his hubris and resists the temptation of the Dark Side. When he es the trials, the Force Priestesses proclaim Yoda capable of retaining his identity after death.
Obi-Wan Kenobi ostensibly sees the famous Jedi Master living on Tatooine, where he retreats after the events of Wellspring of Life would not only provide an exciting excuse to see other planets, but also tie Obi-Wan's story into the narrative of The Clone Wars, expand the lore of the live-action universe, and form a compelling step in his spiritual journey.
When Obi-Wan dies, he too becomes a Force Ghost. Since both Obi-Wan is grappling with his tragic past and his regrets following the fall of the Republic. Having him go to the Wellspring of Life would reconnect him with his roots as a Jedi and provide a heroic culmination in his spiritual journey. Like Yoda and Qui-Gon, he would gain greater understanding of the Force; which, presumably, is what leads to his wisdom and serenity in A New Hope.
Then there is the Tatooine problem. Of course, it makes sense that Obi-Wan Kenobi would take place on Tatooine since that's where he canonically goes after Revenge of the Sith and it is known that he was a hermit there for many years by the beginning of A New Hope. However, Star Wars fans are tiring of the planet, expressing hope that the series will also take him elsewhere. Having Obi-Wan go to the Wellspring of Life to face the priestesses' trials would provide a satisfying diversion and exciting expansion to live-action Star Wars lore. The Force Planet is especially unique because of the blend of classic adventure and psychological introspection it promises for the characters who visit it. Fans will be hoping that Obi-Wan Kenobi will bring the Force Priestess' trials from The Clone Wars to live-action.
