Here is the sensible comment - I dont see anything wrong with asking for the ice cream with desert. I would mention it just as they start to meal service so that they can get the ice-cream out to thaw. Otherwise, it will be stuck to the container for a fair while.

F crew are normally great especially the experience FAs. One chatty FA once brought me a selection of mains still in their foil containers pre-oven so that I could make up my mind a it as not a busy cabin. I'm not that fussy an eater. Honest, Guv!

BA - when its good, it FAB.