#2 - Han dies. There were rumors a while back that Ford would join the case only if Solo gets killed off, likely in some dramatic fashion. No Han means you've got to wipe out a good 90% of the EU stories following ROTJ. He's not the star of many of those stories, but he's there, his relationship is there, his kids are there. Hoping they don't go this route, but the whole Canon conversation makes it seem all the more likely to me.
Personally, I feel that this is most likely one of the big motivators.
If you have stories in the EU set at, near or after the time-frame of the new Sequel Trilogy (or any of the one-off stories) AND you have sold-your-soul contractually to get an actor back for "one last time" - well then guess what? The agreement you made with that actor trumps everything, especially if part of that agreement is that Han dies.
Now I'm not going to say that this is what they're gonna do, but I think if they were SMART, and had already considered a Han Solo one-off movie, they should have contracted Ford to be in BOTH EP7 and the Han Solo movie - that way the Han Solo movie can be legitimized by having the actor who originated the role playing the character one last time. Much like the concept of Leonard Nimoy playing Old/Trek Timeline #1 Spock in the 2009/2013 J.J. Abrams Trek movies.
But that's just my $0.02