Did you mean to include McDonald’s still offering supersize as a choice in the hypothetical?

I’ve seen a type of hot dog where the synthetic meat stick is coated with sweet batter and then fried. The coating puffs* up and makes the whole thing look big. Maybe this is how they would supersize it.

*edit

edit 2: Apparently it’s called corn dog

Wouldn’t be the first time I asked for something like that

Honestly I’ve always been shocked they don’t do donuts… Pre-made, shipped stale, warmed till serving. Cost is probably pennies and can easily sell 1 donut for 2-3$