Yesterday, they were still doing the testing of Pre-check at MDW. From what I could see, all elites were allowed to go into the area off to the right as you approach the checkpoint. There, TSA was giving out the Pre-check instructions. It was very nice.

Of course, I still haven't received an opt-in, so that may have been the last time doing it for me. Seems odd that they would think it is safe to test the system on people who might not be deemed safe enough to participate in Pre-check regularly.