The point of paradoxes like this is to demonstrate that even in our incredibly simple toy models of agents, we still run into issues. These paradoxes help point out weaknesses of the models and act as new desiridata for better models.
Specifically, he calls for a global tax on all capital, regardless of whether it's real estate, financial assets, homes, bonds, bank accounts. That way people can't get around it by shifting their assets overseas or into different forms.
Obviously this would be difficult to implement, but it can be done by individual states, then countries, then by groups like the EU, etc.