On the other hand, federated learning is something that's clearly desirable, a compelling pitch. So you could argue these "technical impossibilities" might be overcome with enough cleverness, eyeballs and complex enough ecosystems.
I don't think we're nowhere near, but it's one of those paradigm shifts that have my ears perked up. I'm curious what'll come out of this, cheering on Andrew Trask and his OpenMined from the side lines!