A week and a half ago Vin Diesel had a meeting with Marvel Studios (pictured right).
Now we learn at Comic-Con that an announcment will be coming soon about that.
Today at the Riddick panel, Vin Diesel answered a "fan" question (actually the last in the QnA) about what his vision is for the future of Marvel movies (keyword being vision?).
It's reported Vin Diesel smiled slyly responding, "There is some very big news coming at the end of this month."
Obviously, the announcement isn't going to be that he is not working with Marvel Studios, but confirmation that he has signed.
It's possible the announcement could be made at next month's Disney D23 Expo.