I seem to recall someone saying that Season 6 was about "comebacks". Assuming that's true, having Rachel's show bomb in LA, and her having burnt bridges to Broadway and NYADA, perhaps the idea is having her return to Lima (maybe as a Glee Club consultant), seeing it as her only option, and then planning a comeback. Maybe finding a way to reestablish herself on Broadway after all (the last scene of the series could be her ready to leave Lima for New York and spending one last moment with Will, reminiscing). That could be a satisfying, even compelling, story line.
But it's Glee, so who the hell knows. .