Honestly it baffles me that in all this discussion, I rarely see people discussing how to do this with appropriately licensed images. There are some pretty large datasets out there of public images, and doing so might even help encourage more people to contribute to open datasets.
Also if the big ML companies HAD to use open images, they would be forced to figure out sample efficiency for these models. Which is good for the ML community! They would also be motivated to encourage the creation of larger openly licensed datasets, which would be great. I still think if we got twitter and other social media sites to add image license options, then people who want to contribute to open datasets could do so in an easy and socially contagious way. Maybe this would be a good project for mastodon contributors, since that is something we actually have control over. I'd be happy to license my photography with an open license!
It is really a wonderful idea to try to do this with open data. Maybe it won't work very well with current techniques, but that just becomes an engineering problem worth looking at (sample efficiency).