I'm not a lawyer; my exposure to employment law came in a previous existence as a workplace union rep and this is somewhat outside my expertise.
As I understand it, if the Uber driver were allowed to have someone else drive their car for Uber when they felt like it, and had the freedom (actual, not nominal) to decide which clients they'd like to take on, and had control of their pricing, then there would be no question it was actual self-employment.
Sure, I understand that. USA law is fuzzy in the same way. (The IRS 20 rules[1] are guidelines and not binary true false criteria usable for perfect machine learning classification.)
But for the sake of discussion purposes on HN, I'd like for you or anyone to play the role of general counsel for Uber and say exactly and concretely what they would need to do.
[1]https://www.google.com/search?q=irs+20+rules