If training data requires licensing fees, ML practitioners will become a licensed field de facto, because no one in the open source world will have the resources to pursue it on their own.

Perhaps a better analogy is movies. At least with acting, you can make your own movies, even if you’re on a shoestring budget. With ML, you quite literally can’t make a useful model. There’s not enough uncopyrighted data to do anything remotely close to commercial models, even in spirit.