I'm not sure whether actually calling the movie "Black Panther" would be the most marketable decision!
Yeah I am sure that alone will kill it with the majority of the movie going public. I have often wonder why they haven't changed it.
I read somewhere that Stan Lee, etc. had considered changing it. I know that at least one of the names they were floating before officially naming the character was Coal Tiger. But come on, Black Panther is a strong, powerful name, much better than Coal Tiger or probably just about anything else they could come up with. Besides, the character predated the Black Panther Party.
I don't think they should change the name. If they do that, why do the movie at all? Do you think people would be more inclined to watch it if they called it T'Challa? Or Last King of Wakanda? Coming to America Too? It will more than likely alienate BP's fanbase or general comic fans that might be inclined to watch the film because they'll be fearful or skeptical of what else was changed.
Keep the name, but market the hell out of it so that a lot of movie goers, who might be turned off by the name because they will associate it with the Black Panther Party or the New Black Panther Party, will get that it's a comic book movie.