US banks would be prohibited from processing payments for those model providers, and those model providers would update their EULAs to prohibit American-usage.

Look at how online poker was "banned" in 2011. It was and always has been legal to play online poker in the US, they just made it illegal to accept wire payments for online gambling which destroyed the American market for it.

So many comments in this thread miss the point; an American "ban" on Chinese open-weights is not aiming to make individual usage impossible and wouldn't be accomplished by throwing people in jail. The point is to make their usage difficult and uncertain enough that large companies will opt for American alternatives.