A "guy," of course, is understood to be a male. If there is a sign on a door in a restaurant that says "Guys," women do not enter. Yet one may hear female servers in that very restaurant address a table of female diners as "you guys."
Even more confusing is the expanding use of the word "bro" in conversation. It is an abbreviation of brother, a masculine reference. Yet increasingly one hears both men and women using the term when addressing women, as well as men.
Should we go with the flow and consider both "you guys" and "bro" to be genderless terms? Or should we pay attention to that shrinking number of women who are offended? I try to avoid both terms in all contexts.
As for the phrase "you guys," that is just another consequence of the problem English gives us because the word you can be both singular and plural. We may know it to be true, but it just doesn't seem right when we use it as plural. We want to add something. And so, depending upon where you are in the world, you may hear "you all" or "y'll" or "youse" or "you'uns" or whatever. The phrase "you guys" may turn out to be the winner, crossing state lines and international boundaries.