Yes, the new trigger is very handy for adapting a layout to changes brought about by rotating an iOS device into a new orientation. You can use Get ( WindowContentWidth ) to detect whether the device is currently oriented for landscape or portrait.
But if you have a single button or field instead of a row of the same, you can select both left and right autosizing anchors and the button will stretch as the pop-over stretches. This fails when you have a group of objects that you want to auto-size as a group. I just made a quick test in FileMaker 13 and what I found was better than what I've gotten in earlier versions, but still not a case of "scaled autosizing" of a group. Instead, one button auto-sizes and the rest remain the same size.