The new tax law makes it very clear that the exchange from cryptocurrency to alternate cryptocurrency is a taxable event.
The difference between the purchase price and the value when you exchange is a good way of thinking about what your gain or loss is. Although prior year like-kind exchange treatment has not been addressed, the IRS is asserting that a like-kind exchange does not apply in the most recent 2018 tax law.
If like-kind exchanges were to apply, a separate Form 8824 would be needed for each like-kind exchange. For my clients who are active traders, that would mean hundreds or thousands of forms to file to report and validate the like kind exchanges prior to 12/31/2017.
The IRS may very well disallow it as the IRS has not issued guidance as of this time. The safest and most correct route based on current tax law is to consider cryptocurrency to cryptocurrency transactions as not eligible for like-kind exchange treatment.