We're actually seeing this play out right now with the server-based age assurance systems which are already widely deployed and mandated under the UK Online Safety Act and laws in about 25 US States. In many cases, the sites just comply, presumably because they are worried that the regulators have a way to reach them even if they aren't hosted in the relevant jurisdiction. In some cases, however, the sites just ignore the regulations or tell the regulators to pound sand, as 4Chan is doing with UK OfCom: https://www.bbc.com/news/articles/c624330lg1ko