if too many people is using bitcoin then government will make rules to tax bitcoin transaction and maybe the government will banned bitcoin, but actually now we already pay bitcoin taxes, everytime i exchange my bitcoin in local exchanger they will charge few percent of my bitcoin
It's unlikely for the government to ban the crypto currency but yes they will sure do impose several rules and eventually taxes. Some countries government has already imposed some laws and some for trying. But for some big governments to impose laws it will require a large amount of people using bitcoin on a frequent basis only then governments will charge taxes.