Nothing i think they will invest in it or even let people who cash them out pay tax because the government always wants money and that is why they would tax it everything but people would still invest in bitcoin.
It all depends on the government itself. If they were mature enough that they actually have a fair idea about what all wonders which bitcoin can bring to their country, then they will for sure go for taking very much positive steps in order to help their people in order to get maximum benefit of bitcoin. Otherwise, they will ban bitcoin and will not allow their people to go for investing in it.