If you check whatever communication made by Satoshi during 2009-10, it is clear that he intended Bitcoin to act as a currency, and not as an investment asset. He hoped that in future Bitcoin will be accepted as a global currency and used by billions of people. But he probably didn't predicted that Bitcoin will be used more as an investment asset, and less as a currency. Now this complicates the whole thing. Currencies are not subjected to capital gains tax. If you do forex trading, a different type of tax is applied. So my guess is that Satoshi never thought about the taxation part, since he never thought that Bitcoin will become an investment asset.