I don't think economies of scale will be lost, they would have more complicated logistics since each country would have its own policies and a deep analysis of the laws of each micro-country would have to be carried out to export... This would be solved with new technology (Imagine consulting a global database if your product is accepted by the policies of most countries, everything would be automated and would have no extra cost).

The micro-countries could create trade agreements with each other (as currently occurs in the countries), such as eliminating import taxes on a product that is in high demand, exchanging resources, pooling wealth to work for a common goal...

Another important aspect would be the judicial system, there could be criminal countries that make theft legal in their territory, if that micro-country is in a strategic place, sooner or later people would have to enter the country... One solution would be for the micro-countries to adhere to a centralized judicial system made up of members from each micro country, similar to how the European Union works.

I have a lot more ideas on this topic, but I am not an expert and cannot validate my hypothesis, or do a deep and detailed analysis of this topic.