Leech should definitely be a teen by now, and perhaps able to refine his power at least as well as he has in the past. He's shut down non-mutants, like Hazard, and people selectively, shutting down a single person's powers, without radiating an aura that affected others, so he should be pretty versatile already. He'd be a fine addition to the New X-Men / Academy X generation, IMO.
And Wind-Dancer definitely needs to come back. We haven't seen her (or Hellion, or many of the others) significantly since her resurrection in X-Factor, IIRC, and she's just too cool a character with too fun and dynamic a power to be left lying around like that. I like her personality being so different. A mix of unsure of herself, and yet a natural leader, not quite so innately self-confident as Dani Moonstar or Storm or other leader-ladies, which was cool, since it made her feel more like a teen, who spent some time living with an emotionally distant/abusive father who undercuts her self-worth with his words and actions. She's not 100% shy and uncertain like early Rahne, not even a little bit afraid of her powers, and yet also not (yet) as self-confident and decisive as Dani was at the beginning, which is cool. She's got room to grow, as a character, which makes for a character with a baked in story arc.
Same with quite a few of the Academy X crew. Hellion had to grow past his arrogance. Elixir was a complete jerk (and as part of the Five is the most unrecognizable to me, character-wise). Dust quite hesitant and unsure of her place (much like Rahne, another orphaned religious mutant girl). Mercury looking for a place, for people to call her own, after feeling like her family had packed her off to get rid of her. Wallflower, hints of a user, like her father, waiting to go off. Rockslide hiding immense discomfort with his new condition under being 'the funny one' or 'the goofball.' Surge had to be aggressive and break a lot of rules to survive her homeless phase and harden herself against caring what other people thought, and now has friends she has to treat better than that... Lots of places to go with that crew.