Working for a fully distributed company it definitely feels like it's not naive. Certainly everything won't go this way but it's a lot easier than most people think. Apart from at setup time and with public holiday schedules those borders are not very apparent.
Companies with 1000s of people have been remote forever. I worked at Autodesk in a team across two multinational companies which on our side were through Toronto to us in Iceland and on to Shanghai. If you think big teams aren’t distributed you’ve not worked in a big team.
It would require a sea change in thinking, or get people comfortable with the idea of not belonging to nations.
As you point out Nationalism has been a pretty recent development. It has mostly been enforced by indoctrination in the education systems and culture. While it has had many many issues, we have seen it reduce the number of conflicts and wars by a lot, and thus it appears to be a reasonable solution.
Whatever solution aims to replace it would have to not only overcome all of these barriers, but provide better results as well.