Excellent points. I think if we broaden our scope to television (which is arguably becoming looked upon just as highly as movies) there are better pickings. There are a lot of characters that are based on sex, but there are a few that could work either way. That's not to say that sex-specific situations don't come up. They do, but that's more because of the need for greater amounts of filler content on a TV show than because of a fundamental basis for that character. So, not as perfect as Ripley, but not bad.

(I don't watch a lot of TV, but Continuum and The Black List come to mind, though neither offers a true Ripley)