Y’all actually has gained particular traction in the north through the queer community. Most trans people I know use y’all even if their geographic location doesn’t indicate they should
"y'all" fills a legitimately useful gap the English language has. Other languages have a word like this.
Edit: also something cool I just found out, some languages have a way to disinguish "we" (you and I), and "we" (me and the rest of us, not you). It's called clusivity and is missing from European languages. Many indigenous languages of the Americas and Oceania have this, as well as Vietnamese and northern dialects of Mandarin.
People where I am from call everyone "you guys" - men, women, trans, doesn't matter, everyone is just "you guys" even when it's a woman addressing a group of women.
The literal meaning isn't gender neutral, but in actual practice, it 100% is.
As for "y'all" or "you all", I don't see how it could possibly be interpreted as offensive to any gender.
I'm from Maryland and I said "howdy" in New York and I got roasted by the CVS clerk for 2 full minutes. And then I said "do y'all have Tylenol" in hopes that she could point me in the direction. Another minute of her roasting me...
Having exported myself from the deep South to Yankee land, "Y'all have a good one!" never fails to brighten the day of someone working a cash register.
In general, folks up here really like southern politeness. They think sugar wouldn't melt in my mouth. I get stopped in stores to talk all the time. Pretty frequently, they just give me a discount. I thought Yankees were supposed to be rude, but they're actually really nice in public.
I’m from Australia and I’ve started calling all groups of people yall because it’s gender neutral… very unaustralian term, and I love so much the irony of iconic southern terms being used to support trans activism
Y'all is the opposite of offensive for trans people. I lived in the south for a while, and I now use y'all specifically to be inclusive. I wouldn't say "you guys" is offensive to trans women, but I would say for me and likely other trans women it briefly brings to mind being misgendered in the past, so I would call it a small kindness to ube as gender neutral as possible.
It feels like a standard case of it's fine until it isn't.
I wouldn't worry about it and only drop it from your vocabulary if you notice it causing harm.
I'm not from the south and use "y'all" all the time. Find it very useful for filling in a gap that English has and slightly faster than saying "you all". Its gender neutral in my opinion.
I'll throw in "folks" as another gender neutral option. I say "you folks" all the time, especially in professional contexts. I'm not from the South, but I have family there so y'all is a part of my vocabulary. I use it in more informal situations pretty commonly.
I can't speak for anyone else, but you seem to be missing the biggest issue with this map: saying "you guys" excludes anyone but those identifying as male. You may not mean it that way, but I've had women be offended when I used that in the past, and I wouldn't like being referred to as a "gal" in a group of women. It's just not accurate.
Personally, for a gender-neutral way of addressing a group, I like "you folks".