Not a joke, I unironically like "y'all". I've never heard "youse" used in the wild yet, but I'm not opposed to it either.
I mostly (only?) know it from humorous or mafia-specific portrayals of Italian-Americans.
As far as I was aware, “youse” is mostly confined to certain British regional dialects, most notably Scouse.
It's endemic in certain Scottish regions, particuarly Glasgow, some parts of Edinburgh, and Fife, alongside other made up words like 'jamp' (past particle of jump). We're devoted to mangling the English language.
Definitely used as a plural though.
Also, there are variants in Northern Ireland - where my uncle's rallying cry is:
"Are all of yousens' coming?"