Afaik capital gains taxes only apply when you sell an asset where which in government terms means selling Bitcoin for fiat. But that's not what you want you want to pay for things.
Discussion
There are regulations in many countries that also want to tax “unrealized” capital gains, which would tax you on the assessed value of your unexchanged BTC (and homes, cars, etc). I guarantee that, right before BTC actually takes over, the fiat system will fight for THAT to stop the change.
It doesn't now. It not what's keeping Bitcoin.
This is incorrect for USA/IRS