There's not much uncertainty for business really. If you're pulling the moves that Apple and other companies pull to "optimize tax", then you are with 100% certainty trying to game the system and violating the spirit of the law.
It is 100% untrue that "the spirit of the law" isn't factor in the US judicial system. The main way it enters explicitly is through courts taking into account the intent of the legislature. The most notable example of this was the way US courts interpreted the 14th amendment, which was far from it's literal statement.
Even if it was retroactive, which it is not, being punished for premeditated tax avoidance can hardly be called unpredictable.
The central difference of opinion is of course whether outright gaming the system is acceptable regardless of the written rules being followed to the letter.