That seems strange. Typically with stocks you only get taxed on your gains once you sell the stock for USD. Trading one coin for another seems different since you never monetize the gain and just reinvest it. Perhaps they plan to treat the crypto more like currency than stocks. In any case, I don't plan to sell very often and I am sure someone will come up with a way to do crypto to crypto trades without needing to have an exchange account. At least I hope they will.