Jennifer Lien's character, Kes, was written out of Star Trek: Voyager at the beginning of the series' fourth season. It made way for Jeri Ryan's Seven of Nine and the accompanying storylines of a rescued Borg drone. At the time, producers said they'd run out of storylines for Kes, and so she turned into a non-corporeal being and left Voyager.
Screenrant's Jen Watson describes an excellent way for the character of Kes to return to the Star Trek timeline, and it sounds entirely feasible. Her story did wrap up quickly, and then Voyager brought the evil Kes back which was an even worse way to say goodbye to the character. So maybe there's something to be said for revisiting Kes.
However, because Kes didn't have strong storylines in Voyager to begin with, would there even be a purpose for bringing her back? Would it be to give her a proper sendoff after the atrocious way Voyager brought her back in "Fury?" ? Is that necessary at this point? Or perhaps it wouldn't be the sweet Kes returning but a version of the character from "Warlord," the a season three episode where an evil warlord overtook Kes' body. That Kes could bring all sorts of trouble to the Federation, and writers would have no trouble finding storylines for her.
While there is a good case made for how Kes could come back, the issue is whether or not her return would actually benefit a Star Trek series, or would it simply be fan service for those who really liked the character? Whatever the case may be, if the sweet Kes does return to any of the quadrants, there has to be a strong reason, and hopefully, a good writer to give her a storyline that doesn't feel like the character is being shoe-horned into a series.