As for Emma. It would be a waste to keep her alive and made her Shine Like a Diamond, in that episode for her not to comeback. Emma is a really popular X-Woman in the comics, and has been made a regular X-Men member in Wolverine and the X-Men and X-Men Anime, so it won't be new if she's running side by side with the X-Men for the next season. But I would save her joining the team for the third season.
 In terms of new X-Women, there aren't too many choices. Psylocke and Shadowcat are next in line after Storm, Jean and Rogue, in terms of general importance in the X-Men mythos. I would like to see them both join the team before Emma. Polaris, Dazzler and Rachel are B-tier X-Women who don't really get the spotlight outside of the comics. So I don't see them being added into the team. Armor, Cecilia Reyes, Sage and Marrow aren't huge names in the X-Men comics and I can't see them taking a spot over bigger names. X-23 is a Wolverine clone and why include her this early for the 2nd season. Magik should be utilized in the New Mutants team and Domino should be in X-Force. So its really either Psylocke, Kitty or Emma for the fifth X-Woman role.