I like this. A possibly simpler example is where A is a 0 or 1 output of the AI, B is the output from an antagonist who gets to see A, and utility is XOR(A, B). Then B=A (by antagonism), so standard utility is always 0. However, according to your def, d with A having a 50-50 chance of 0 and 1 would be optimal, with modified expected utility of 0.5.
I like this. A possibly simpler example is where A is a 0 or 1 output of the AI, B is the output from an antagonist who gets to see A, and utility is XOR(A, B). Then B=A (by antagonism), so standard utility is always 0. However, according to your def, d with A having a 50-50 chance of 0 and 1 would be optimal, with modified expected utility of 0.5.