I am interested in thought on this topic, hypotheticals:
1) What if a small / medium / large country central bank begins accumulating
It will likely raise the price of bitcoin to a certain extend.
2) What are the chances of this ever happening?
Small. I don't think the a country's central bank will be accumulating bitcoin
anytime soon because the price of bitcoin is not stable.
3) How much would they buy?
If they ever buy, I think 1 million bitcoin will be a good start.
4) What would the effect on price be?
Again, it will drive the price of bitcoin for a bit.
5) If it is a 'rogue' nation, would it kill bitcoin?
No. it will not kill bitcoin because because is global and not just tied
to a certain country.