Yesterday I was presented with WeChat's Cookie policy for European users [1] for the first time, and they appear to have a European subsidiary, which could probably be fined. Of course they could just decide to fold that operation, especially considering (IANAL, but) the policy doesn't appear fully GDPR-compliant. I doubt that they are making significant profit in Europe anyway.
[1] http://www.wechat.com/mobile/htdocs/en/cookies_policy.html
GDPR could become a global thing, because it could be used by the EU as a predecent for Free trade agreements. (which most nations in the world are happy to sign).
It could, but with controversial concepts like "right to be forgotten" baked into the GDPR, I don't assume most nations will necessarily be happy to sign "free" trade that requires them to rewrite history records.
If such a fine is levied, but the company is based in China, does China have any treaties with the EU demanding the fine be enforced, or can they tell the EU to go pound sand?