Unless they could somehow find a way to tax bitcoin, the governments would never accept it. Big companies may as it could be a good way for tax evasion but unless governments could benefit from it somehow, it'll never be accepted.
It will be based on use. They can tax it when it is used to buy goods electronically because retailers will have proof of payment used. Government takes it in BTC or has the retailer convert it to fiat for tax purposes. If government will take BTC, I can see BTC price manipulation to get the price up for when they try to convert it to fiat.