I like to think of the Roman Empire as in a time when people would move freely between the expanses of the empire if they wanted to. North Africa to Europe, Europe to Asia Minor. No passports, no visas, and a complete melting pot of cultures and people.
In reality, the major migrations were probably more to do with slave trade, conquest and economic promise, but I think it is a good example of your point that people have always moved.
The interesting question to me is whether the world is genuinely becoming more integrated and culturally ambiguous (due to factors such as internet, cheaper cost of travel, etc.) or whether the world is gathering more pressure (from the top-down) to separate and exclude. My feeling is that while there are a lot of people free to move and be ‘world citizens’ (I hate that term), there are also increasing proportions of people who are explicitly excluded because of it. Take the EU migration laws for example, as the EU opens its (internal) borders to new members, it is effectively alienating those who are not (and may never become) members.
I think you’ve touched on really relevant points to do with identity and the ageing frameworks on which nationality are built, but I can’t help but point out that (because I’ve thought this about myself) it’s a point of view coming from a privileged position. I’m not sure that we can take it as a given that “more and more people [will] gain the freedom to easily travel and communicate globally”.