There hasn't been a country who said that bitcoin is totally "illegal" those who made some regulations are China, Usa and probably the India, but they didnt said that bitcoin is ilegal, a regulation is something completely different. Just remember that China is not killing anyone just because using bitcoins, they are only shutting down some exchanges in their countries, but nothing more.
Bitcoin is legal in most countries all around the world.
Legalizing Bitcoin is subject to a deep research and study. This will depend on what economic system a country applies parallel to what regulation they will imply that would fit their system. Surely, they will consider their existing tax laws or reforms if necessary. They will find ways how to makes this work because we are entering the digital era where everything is done electronically to adopt in future market world.