Seven definitely has the most fertile ground to cover (meeting Hugh, joining the Fenris Rangers, the implied background with Bjayzl...), though particularly with the end of the season implying she’ll be part of the crew going forward, I’d kinda like to see something relating to, say, the Raffi-Rios friendship or even post-Romulus through the eyes of Narek come first, let the Seven story be more of a lead in to season two.
I mean, it’s not like they have to be mutually exclusive or anything, and given that Seven is a popular character, it’s a no-brainer that it’s coming, but I’d like to see the new characters get some deeper development before we return focus to a well-established one, even if she’s been through enough to argue she has become a different person.