Thanks for your interest. My thoughts are not extensively researched so inevitably this idea will generate problems of one sort or another that need imaginative solutions. But briefly, this is how I would respond to your comments:
1/ This is actually part of the inspiration for this idea. It’s obvious that there are many millions of people looking for a way out of many difficult contexts. Provide any way, and millions will come. If any rich Western country said ‘all are welcome’ the sheer numbers will rapidly cause them to think again. So my idea of ‘Free Cities’ was not a proposal to establish a single city, but a template and a formal legal status for cities of this kind. In the hope that not one, but many might be created, by many different actors, as an attempt to align different but comparable interests. China, for example may see some advantage in creating a ‘Free City’ that aligns with its overseas investment plans. The EU, or members thereof, might see a ‘Free City’ (or two) as a much more effective context in which to address the humanitarian crisis emerging from Syria.
In the long run, I imagine ‘Free Cities’ could be simply an institutional mechanism for dealing with inevitable population flows, which are only going to increase. A problem I foresee is that it would need to be accompanied by a moderately interventionist international stance because whole populations may decide to leave a war zone, or entire minority communities might be eased out by governments with bad intentions.
Equally, in the long run, I would hope that ‘Free Cities’ or something like them could provide contexts in which people can at least continue with their lives to some extent, rather than existing, parked in some desperate refugee camp from which there is no obvious way out. Some may be very successful, but others perhaps less so. In each case, they would give people a quasi-status, freedom to return if they left to visit their homeland, and if managed properly, good education opportunities and access to the formal immigration mechanisms of other countries.
2/ This seems like a practical difficulty but one with patient solutions. I imagine each city would have a formal language, and could slowly ensure that all have moderate command of it. Equally, cultural differences just have to be policed carefully. This has been done all over the world, and surely lessons could be learned about how best to do this. The interesting thing might be what cultural intersections emerge. It’s an important problem, but I think there are many countries that have long experience of dealing with matters of integration and legal equality.
3/ I would say that it creates obligations, and with proper monitoring these are not insignificant. However, right now, the UK (for example) funds large amounts of refugee camps with no end in sight, usually through the UN. A ‘Free City’ could develop its own economy and attract investment and jobs. Therefore, although there would always be important obligations for sponsor countries, the point is that the ‘Free City’ would allow for some autonomy. Hong Kong, for example, is much richer (Per Capita) than the UK and was always self-financing. If the ‘Free City’ never really develops its own economy though, then even then it should provide a better and safer context for managing the aspirations of desperate people.
As an aside, I noticed recently a story about Hong Kong in the 1980s. When the handover of sovereignty was in view, and the UK was concerned about the (ostensibly British) population of Hong Kong being reluctant to become Chinese once again. Several ideas were discussed to give them a home elsewhere. One idea was to lease an island from the Phillipines and set it up along similar lines to Hong Kong as a UK Overseas Dependent Territory. This may have always been unlikely, but interestingly, it was vetoed by Singapore on the grounds that they did not want the regional competition this would present for Singapore’s development model. In other words, the Singaporeans were not under the illusion that it wouldn’t work.