My experience as a data point: A few months ago I flew BOS-HKG in F accompanied by the 21 year old daughter of one of my friends in Y (we'll call her Susie). She had never been outside the U.S. before. I was the only one in the F cabin (which meant that they were happy to set the temperature where I wanted it, -- 17º ^^).

As I was getting settled after boarding and before pushback, I told the cabin crew member who was helping me about Susie. Didn't ask to have her join me at all; because I know that it's neither appropriate nor allowed. Didn't ask for any special treatment for her, either. Cabin crew member got a CX duffel bag and filled it with various goodies, including snacks, F pajamas, extra blanket, etc., then walked it back to her in the Y cabin. She came back and told me that she also moved Susie from a center seat to an aisle (which worked out just fine, as Y was nearly full and Susie was up and down to the lavatory, spending most of the flight being sick to her stomach), as well as alerting Y cabin crew that she was traveling with a One World Emerald pax.

Consistent with upthread reports, Susie was brought up to 2A when the landing sequence started (I was in my favorite seat, 1A), and for the duration of the flight so we could deplane together. Walking off the plane, Susie told me that the cabin crew in Y was incredibly solicitous of her, which she especially appreciated given that she spent most of the flight sick to her stomach.

All-in-all, it was a great experience for both of us, and cabin crew couldn't have been nicer.