I've just been talking about this on a thread about adding a vegan trait.
We could definitely do with a quick way of finding out dietary requirements from other Sims. If you're at a festival or club gathering and you all grab a plate together that contains meat or dairy and it makes someone ill or if you're cooking for someone and don't know their requirements it can put a dampener on an event.
If not added to likes and dislikes it could be automatically displayed somewhere even before you've fully got to know someone. I know traits are usually learned as a friendship builds but maybe dietary requirements could be treated differently. It could even be shown when you are choosing a group for a social gathering maybe. It could be displayed with a symbol in the corner of the Sim photo that matches the symbol of the personality trait.