DeviantArt already tried. It was somewhat controversial.That's where we disagree pretty strongly. Which is cool. We are allowed to disagree.
One way I thought of that could (probably will) manage to make generative AI more legal and even less ethical is when all the image storage service (iPhoto, Deviant, whatever) add clauses to their TOS that the owners of the pictures allow the company to use their images for training AI. I bet that is coming.