I think it would be wildly different.

Maybe it would be a space where users can straight up post pictures and move them around in a large space. Not pixel by pixel, but a whole image at a time, in a space big enough to fit thousands of pictures.

Maybe it would be a collection of symbols and flags where users add a dot below what they identify with.

Maybe it would be a shared drawing canvas, where users can do freehand lines, outlines, and fill with colors like MS Paint, but all at once and over each other. Basically an internet graffiti wall. To align with the ideas of Lemmy, it would be possible to "wall off" off bits of the greater canvas, and block the rest of the users so that only one community/magazine /server can draw on that space, while any unclaimed area stays wide open for anyone.

Maybe it would not exist at all, because the whole mentality of the Fediverse might not support enough collective expression.