Don't bring the two together because they are different things entirely, visa serves the purpose of an access, permission or authentication that permit one to travel out of his country to another one, this is a strict procedures that link to the apprehension of those with bad records to be denied access to travel out, while bitcoin is a digital currency who's main purpose is to free us from the government and all centralized body in handling our finances in the world economy system, bitcoin can be an acceptable means of payment of service while trying to travel out but cannot service an anonymity where physical representation is needed to travel out of a country, i understand what you mean as regards privacy but here you're appearing in person to travel out of your country and a currency cannot just perform your clearance in giving you access of entrance into another country else many with bad reputation will flood and abuse the process.