Honestly, outside of Wolverine (and even then, only barely) and Deadpool, I don't personally think
any X-Men characters are strong enough to support their own solo movie. They work well in group settings because the whole point is to see each of them work off each other, but individually? Again, outside of Wolverine and Deadpool, none of them have been able to support a solo book for long. They're all usually cancelled within a year. Cable was a weird exception, I suppose, but his book was strongest during the 90s, so that's not that surprising. But none of them really have a deep enough mythos of their own to sustain an ongoing book or potential solo movie. Few of them have key archnemeses of their own. As weak as many of the solo Avengers villains are (like Iron Monger or Malekith), there's at least enough history of solo stories to pull from. To make a really good solo X-Men movie, Hollywood would have to be more *gasp!* original! And that probably terrifies Hollywood.