bitcoin are valid. But you can (and should) register your wallet in a central database.
And payments for goods and services are only allowed from registered wallets.
Unregistered wallets are treated as secret bank accounts, and no registered wallet is allowed to accept any money from any such account. If they do the owner goes through a lot of trouble (among them confiscation of any bitcoin sent to them), unless they immediately forward the money to their government.
Considering how easy it is to trace and backtrace transactions, it seems a plausible solution for the governments that will essentially recreate the status quo except with a currency that cannot be printed on demand.
How plausible do you think this is?
What would the effects be?
So the US and EU would dictate to the Chinese, who are the main users now, what they can and can't do with their own money?
I don't see that as a likely scenario at all.