I would argue that Bitcoin is the coin, not a national cryptocoin. Russia world not trust a US coin, the US would not want to use a Chinese coin, etc. Bitcoin is effectively neutral territory but is effectively controlled through centralized mining operations that can certainly be collectively monopolized by the largest sovereign nations. It would be the modern version of mutually assured destruction.

Bitcoin is already a reserve currency in crypto thanks to longevity and stability of the protocol. Another may become the primary transactional currency and there may well be national variants for local trade, but reserve is effectively established.