It doesn't matter what the EU purports, that's nothing more than a comical fantasy on their part. I live in the US, my business operates in the US, I operate by US law.
It also doesn't matter what China purports I should do with their citizen data, or South Africa, or Australia, or Brazil: their wishes don't overrule the supremacy of US law inside the US. If China wants me to delete everything on my service about Tiananmen Square, or an anti-China activist, guess what, that's not going to happen for the exact same reason. I'm also not subject to the UK government's enforced media blackout on the Tommy Robinson arrest: they too can piss off.
If a EU citizen signs up with my US based service, their data will be governed by US law.
It is that simple. It will remain that simple. The US isn't going to cede its sovereignty to the EU: it's drastically more powerful than the EU in every regard. There is no scenario where the US lays back and allows the EU to legislate how the domestic US economy operates in such large ways.
The only likely outcome is that the US comes up with its own new privacy rules in the next few years, which will be different - more lenient - than GDPR. If you want to operate in the two markets, you'll have to comply with each approach accordingly.