The destruction of Earth has obliterated the the twentieth century (and onward) nation-states....and replaced it with geographical localities of Mars, Venus, the Jovaian moons, etc., which occupy varying levels of nationhood. So the concept is definitely still around.
Worth noting that nationality as an ethnic and cultural concept, has endured is pretty darn strong in the Solar System. Every settlement we've seen has embraced some historic idea of nationality (this is probably more at home with the Soviet and Eurasian definition of a nationality--a historical people, a homeland, a written and spoken language--than contemporary American ones). What's really telling is that, in specific cases, a resident national identity has endured in the face of heterogeneity of population. So, the asteroid colony Tijuana (aka T.J.) is very obviously Baja California and Northern Mexican inspired. But there are very clearly Asian languages being spoken in addition to English and Spanish.
This doesn't really refute your point, but I thought it was worth noting. Nationality (or as we might call it in an American context, race) endures pretty strongly, even if sovereign nation-states were all turned to dust when Earth was (mostly) loss, and have been replaced (Europa has a sovereign government that's called..get ready for it...the European government!) by weaker but very similar institutions.
On the other hand, I'd never considered that Vicious might be Chinese (in fact, the most I'd ever thought about it was that Vicious might actually have a similar background to Spike, a Martian, but had changed his appearance somewhat over the years). I actually really like that explanation, even if it can't necessarily be confirmed.
