If Ant-Man can get his own movie, surely Black Cat can. Overall there's really a lack of a good female hero movie. The Catwoman movie with Halle Berry was lol, the Elektra movie was lame, the new Wonder Woman of the DC universe looks (beforehand at least) like a joke, and maybe we will see a Black Widow standalone movie, maybe not. If you go to earlier movies, it doesn't really get much better. I mean the Super Girl movie is just awful.
So with this said, I think there is a market for a really good female super hero movie. I would imagine there's plenty of girls/women out there who might not care much for the super hero movies because it's mostly dudes, but who would be interested in a female protagonist. So I mean, if they had a good script and a good idea, I think a Black Cat would not only be doable, but it could be a hit. We haven't seen that many super hero movies with a female lead, and especially nothing noteworthy quality-wise. So why not?