I can't tell if he was joking or not... the James Bond shyt was clearly a joke but the blogs/websites are reporting it as fact... The thing is (as far as Black Panther goes) it could work in a way that would work for him. He could play the father of T'Challa (T'Chaka) on his last days as Black Panther before he passes the torch down.
This is what Vin Diesel tried to do with his Hannibal biopic... he wanted it in 3 parts and wanted Denzel to be the star of the first movie with the focus on him as the father of Hannibal.
As far as the Seven role goes... you have to understand the ONLY other notable movie Fincher had his name attached to at that point was Alien 3. Can't exactly blame him for turning Seven down... when he was coming off of movies like Glory, Much Ado About Nothing, Pelican Brief, Philadelphia, Malcom X, etc. He wasn't taking those risks then and I know the violence is the main thing that turned him off of Seven. The thing is.. he probably wouldn't have done Training Day if he had done Seven....