Cannot do this because Bitcoin is fully decentralized and they even don't know the creator of BTC then how then can ban BTC. China tried to ban BTC in their country but did not succeed. Government can only ban on crypto related transaction from credit card and bank but alternative of this P2P is available. So as far as I know it is not possible without damaging all Blockchain codes.
 Second only some country may be ready to do this but not all because two countries already adopted BTC as a legal payment then how they will help to ban crypto? If they do, they are shooting themselves in the foot. Banning Bitcoin is not solution. India already announced 30% tax on crypto so don't think they will in favor of banning BTC.