This discussion on GPLv3 between Javispedro and Olf is very interesting to a noob like me. (even though it escalated a bit at the end )
I would not say that one won over the other but I tend (with my zero knowledge and so without weighing anything in the discussion) to be convinced more by Olf ;-)
And I believe even tiny Jolla paid quite some bulk to some lawyers over the years to try and find the best way to deal with it. I have difficulties to believe that they avoid GPLv3 for nothing.

Regarding Qt 5.6, I have one question: If Jolla pays the commercial license to the Qt fundation, that means I guess they can avoid GPLv3 for the Qt pack. Do you think they will go that path?
Because I do not think to have Qt5.X above 5.6 can be optional...as done for bash