Then the company in question will have to decide which market is more important to them and follow the rules of that market, while not being present on the othe

Then the company in question will have to decide which market is more important to them and follow the rules of that market, while not being present on the other. Others have already noted the risk of a trade war following from that, but that doesn't preclude the EU/US/China/.. from still doing it. It's just a matter of how important they think the rule is.