jubilee, as jury said, represents a very important concept within the marvel universe, as a 'defenseless' person with meager powers and naivete to fill the oceans who is attempting to come to terms with herself as both a person and a 'superhero.' as such, she appeals to a certain target group that would otherwise feel largely unattached to the comic book culture, and is quite profitable.
emma plays a very important role within the series, especially growing in importance since Gen X, and would be a horrible choice. she is the antithesis of Jean, in all ways outside of power (which is certainly not coincedence,) and as such creates both a loving following, and a 'hating' following. both marketable and tactically useful, she's an asset despite the popular opinion.
i'd, personally, have magneto kill gambit. i lost interest in remy after belladonna disappeared, and i just feel like he's served his purpose. while it would create a large fan uproar, because he is 'so popular,' it would also gather interest in the remaining characters as a display that no character is permanent. and, as for magneto killing him, i bought into his relationship with rogue (in the AoA) much more readily than remy's in 616. also, magneto's ability to touch rogue without consequence seems much more natural, and less 'manufactured,' than remy's power application in that regard. but that's me.
And seriously. Jubilee isn't that bad. She's actually decently powerful. Apparently no one has read Gen X. She can shatter steel with her "fireworks". I dunno, that seems pretty decently powerful to me.
Now, who really should go is Maggot. What the hell. I love everything about X-men, but some characters...it's like Marvel was just spinning around in circles and throwing darts at a wall to figure out what new character would be next.
But that's just me.