BLACK CAT is a worst idea than putting VENOM in SPIDER-MAN 3!
If they go ahead with putting Black Cat the next film(s), it will further concludes that Sony, Raimi and MARVEL are wrong for the Spider-Man movies. That they have no idea what the hell they're doing, and fact that they lack focus, direction and a clear vision for these films. Choosing the wrong villain(s) for SM4 could mean delving deeper into a broken franchise creatively--and spitting out the Batman and Robin type films that ruined the Batman franchise.
Sadly, although I hate the character Black Cat, or should I say CATWOMAN. I think Felicia Hardy would be a good addition. Unfortunately, we've seen so many damn LOVE TRIANGLES, where could they possibly go with the character that we've haven't seen yet? The Spider-Man filmmakers are not smart enough, to add a new female character without making her apart of a freakin' love triangle. There has been a love triangle in every film released. At what point do these writers realize that people don't want to see the exact same story/movie within every movie of a franchise. We want to see something creatively different, that takes elements from the comics, that's turned into a complex and mature film.