That assumption is reasonable but unfortunately wrong. The laws around spinoffs are specifically written to apply only to securities (stock in a company) and cryptocurrencies are not securities.
I don't know who's downvoting this, but this is exactly what my high-paid CPAs told me. I'm hoping the IRS gives guidance, and I'm extra-hoping that they give sane guidance, but the law simply doesn't appear to allow for treating coin splits like stock splits.