I don’t think this works any more. I had IN on the long haul to Europe and XN on the domestic leg. Successfully waitlisted the domestic leg to IN. Availability opened as IN4. Chatted 3 agents and called 2 can’t do anything. Last agent on the phone said she didn’t see availability, then asked her to try book new flight on that leg and she saw it. She called support, they said they’d honor it this time, but they don’t do that anymore pricing on mixed class tickets are for the mixed class and that shed leave “a training note for the agent who did the waitlist”.