One aspect of the IRS guidelines that people often overlook, including many CPAs, is that the rules cover "convertible" assets. Most altcoins and especially forks are in no way convertible to fiat or goods/services. You can't place a fiat value on something that is not directly convertible.
In the case of BCH, many people have no way to convert it unless they sell it for Bitcoin and then sell that Bitcoin for fiat or goods/services.
If I forked bitcoin on my desktop computer tonight and sold .00000001 of the new fork coin for $100 bucks, would that mean suddenly every holder of 1 BTC suddenly owes taxes on 1 Billion dollars in "gains?" There is a real lack of guidance in what constitutes as a convertible digital currency at this point. With so much variance in market availability, liquidity, and price discovery there simply is no way to reliably or fairly determine tax obligations on these sort of things.
Ultimately, if the IRS wants to achieve maximum compliance and avoid litigation, swapping should be considered a "like-kind" trade and all digitial currencies should be taxed at the value they are given when converted to fiat or used to purchase actual goods or services. The cost basis will then be calculated based on how much was paid for the initial coins. In this scenario, many successful traders would eventually be taxed at the full value with zero cost basis.
That is a windfall for the IRS and a fair and simple way of gaining compliance.