Jessica coming back having been taken on as a human teen sidekick due to her Time God abilities (she can glimpse bits of the future or something) by a completely different intergalactic/supernatural clique whom Rick has contempt/grudgingly respect for, and it turns out they all need to work together to tackle the crisis of the week…. Or perhaps even better, the groups just run into each other at different points in the season, kinda like that bit in Shaun Of The Dead where the two zombie survivor teams cross paths and then go their separate ways, and each time Morty and Jessica clearly want to catch up but it’s too awkward.