Wow, just think about it how much money will go to Obama... Now IRS may have the best interest to keep Sotoshi safe, whoever he/she is. 
How it has not been converted to FIAT so they have no way to get him for taxes.
But in theory, it is taxable income. Just like property tax, you will pay eventually. That is what I am saying, before Sotoshi pays, irs has the best interest to keep him safe.
Eventually yes, if he even uses it.
I am not sure how all that tax stuff works like with stocks when you make profit off stocks and turn it into more stocks ect ect... the only real example I have from real life is the 401K which from my understanding is not taxable as long as the cash never hits your hands... so I imagine this would fall under the same rules.
401k is created by the congress to set an exception to the general rule that all incomes are taxable. You can defer your payment of tax when you retire, so as to give you an incentive to be financially responsible for your retire life.
Bitcoin, if you treat it as intangible property, than there is no legal barrier for levying income tax when the income is realized. Even better, irs may pass a rule to realize bitcoin is income itself as it is currency in itself!