A well known country with diverse holdings like Switzerland with its huge stake in Apple could perhaps dip a toe.
Gold stockpiles are reported although one could guess not every country publishes its stake very accurately.
Is it possible that some clever finance ministers start accumulating and perhaps don't bother with putting it on the books? Is it even possible to buy in any reasonable quantities?
It could fail, but if it doesn't, they could buy a huge stake of power in international finance for pocket money. That would require the dreams of the Church of Satoshi coming true.
Just remember that countries last a long time and can hodl for a long time.
Crypto-revolution antifragility
It would be very embarrassing to show they bought into an obsolete money with hard earned and taxed cash.
Bitcoin isn`t big and trusted enough to be used as a reserve currency for any central bank.
Central banks don`t need a currency like bitcoin.They buy gold and government bonds.