I actually have been using y'all in this manner for about a decade. I found some women didn't appreciate being called "you guys" when I addressed a group of people.
I'm trying to be more conscious of it because i noticed my friends who are trans make a point to avoid "You guys". I'm resistant to y'all though, so instead of biting the bullet and adopting the local dialect, I'll say "you all" or "You two". Don't do what i do, y'all is kinda useful.