Before Lucasfilm was sold to Disney in 2012, Lawrence Kasdan (screenwriter for 'Solo: A Star Wars Story' and longtime creative force to the franchise) had signed on to a Han Solo movie that George Lucas was developing.
'The Force Awakens' ended up being time-consuming for Lawrence Kasdan, which lead to the addition of his son, Jon, onto the creative team for 'Solo'.
"When I was done [Episode VII], I was sort of burned out. And I said, 'I don't know, do we still want to do this Han thing?' And they said, 'Yeah! We really want you to go ahead with Han.' And I said, 'Well, my son, Jon, is very enthusiastic and full of ideas about the saga.' And he had directed two movies and had done other things. 'What if he came on and worked with me? Because that would give me a shot in the arm.' And so, that's exactly what happened. They made a deal with Jon, and he and I have been writing since, for three years." — Lawrence Kasdan