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.
They may impart tax on us but dont you think they will not be going to do it. Why I am saying this, the reason is, bitcoin is decentralized and this feature dont make bitcoin easy for transactions at governmental level. They always want to circulate money in country according to their own rules but bitcoins will definitely cause disturbance and re balance, hence I think it will take much time.