If the IRS agrees to rewards NOT being treated as ordinary income when received they will most likely rule that the basis in the rewards is zero which means coin holders pay taxes on all gains the coin makes when sold. If sold short term the income would be treated as ordinary income anyway.
It seems removing income tax when rewards are received just postpones taxes til a future date when the coins are sold. It doesn’t really eliminate the tax.
On the other hand, if you always stake and never sell then there wouldn’t be a tax obligation if IRS adopts Cardano’s recommendation.