It is a safe movie (though how safe can it be without Ford playing the role which made him an A list movie star and who defined the role?).
If Disney is considering Indiana Jones without Harrison Ford, I don't see any problem with another actor taking over as Han Solo.
Yeah well.. as many problems as the Abrams Trek movies have the casting was perfect, especially Pine as Kirk and Quinto as Spock (at least in my opinion).
It is doable but you'd have to find a young actor with similar charisma and currently none come to mind except Chris Pratt who's everybody's darling currently but in my opinion too old for the role (especially once they start shooting the movie by which point Pratt will be pushing 40).
However his Starlord already was a Han-esque character so we know he could play the loose cannon with the skills and the heart to match.
Casting news should prove very interesting once the Solo movies gets into gear.