ya (yuh) is the singular of ya'll, being a contraction of "ya all". As in "are ya all here?" Clearly the meme was addressing just a single person. Had it been addressed to a group, depending on size and composition of the group as well as situational context, we would have accepted:
"and ya'll prolly ain't gonna like it"
"and all ya'll prolly ain't gonna like it"
"...nya'll pry'aint gunna like it..."