China only prevented people and organizations from laundering and scammers. Since ICOs are established and China really let ICOs in their country, I think the best way to do is investigate those who are scammers and let them outside the organizations. You cannot prevent or stop people in using or investing in alt coins. There are many alt coins that people have trusted for years.
By doing an investigation about who really are the scammers, I think that would be a long time progress to do since they need not to just go make an investigation, they also need to be inside that organization to be able to identify if that specific organization is not doing what it suppose to do.
That is true that many altcoins have already the trust of these people but since some of the ICOs are just fake demands or something, so still there are things that needs to consider.