Hmm, less people will play it because of the rating but then more people will play it because of the rating. Probably more people that will be turned off (i.e. kids who can't get their parents to allow them to play) so it's probably a good thing because it raises the average age and reduces the amounts of kids, though probably not by a big percentage.
Also helps that parents usually are more against their kids consuming media with anything overly sexual in it than they are against violence.

Though for the title itself, M rating sounds good. I'd be concerned if it would get past that because when titles get past that rating it is rarely out of necessity to tell a good story or enhance gameplay but mostly just to show off guts & gore for the splatter fans and the kinds that think it's the height of awesome.
Same for sexual themes, M rating means they don't need to pull punches and can gives us these kind of outfits (though admittedly some decent female clothing that does not reveal a large amount of skin would be nice once in a while) but it's still a log way from emphasizing sexual theme like e.g. that nude mmorpg where girls with boobs bigger than their heads run around showing off just about everything.

Both would just distract from the actual story and gameplay if it was enough for an 18 and up rating