There is actually two very different questions :
What kind of dialogs do you dream of ? imagination has no limit as has already been stated in this thread.
What kind of dialogs would be both feasible and popular in the next 2-3 years ? This is the real deal (GPT-4 is around the corner)
It would be interesting (and most helpful for your project) if one of the FAANG released a detailed study on how people really used assistants in 2022, at least some kind of Top "vocal commands" list.