If this really materialized then other country will watch closely on the result since it will need some time in able to check the outcome. The question here is whether US is willing to become trial version country for this kind of risky move?
I’m sure many country will follow if this proposal is proven effective. I’m more concerned if this proposal will be accepted rather thinking on what will be the move of other country.
If the United States officially makes bitcoin a national reserve, other countries will quickly propose and adopt this idea to catch up with the United States. They won't wait or spend time monitoring results before making a decision because the United States is not El Salvador or any other country, they are the world's leading power. They are the world leaders, the world economy depends on them and they are the ones who decide the fate of the economy. So whatever ideas they come up with will be recognized by the world regardless of whether other countries like it or not.
Do you remember who came up with the idea of abolishing the gold standard and forcing the world to use USD? The power and influence of the United States is much greater than many people think and they can do anything as long as they think it is right.