I think the more reasonable assumption is that the practical needs of the biggest users will probably trump what any specification demands. The thing stopping

I think the more reasonable assumption is that the practical needs of the biggest users will probably trump what any specification demands. The thing stopping the compiler from doing dangerous behaviours in response to commonly abused UB is obviously that people wouldn't use the compiler if it did that. Just like how the thing stopping the compiler from doing dangerous behaviours in response to spec-legal code is that people wouldn't use it if it did that.