Been "in the works" for at least five years now. Wesley Snipes wanted to do it and play Blade. He even chatted about it publicly. This was before Blade Trinity.
I still say they could and should tie BP in with the Avengers movies. Vibranium could be explained to Joe Public as being of Asgardian origin. A 'magical' metal falling to Earth and having an isolated, yet advanced culture build around it has the makings of a great story.