I agree it should be added if it has not been added yet. If someone asks, "Ты уже дома?" It literally translates to, "Are you already home?" Which implies that the speaker is surprised because someone has come home earlier than usual. But what it means is, "Are you home yet?" Or, "Are you home now?" (As compared to before, when you weren't yet home.)
I also thought this was a very unnatural translation. I think the only way it can stand is in the sense of a surprise exclamation : "You want to have breakfast already"???" as if the person had only just eaten some kind of proto-breakfast and shouldn't be hungry yet! But pretty weird, I'd say. :)
I know a lot of time has passed, but I just came across this post and I am a bit interested myself. I don't know the answer, but I'll just poke the thread. My first guess is to say you should use the subjunctive mood (using бы + the past tense of the verb) however I believe this implies a condition of some sort (I would have wanted breakfast, but your food is awful).
The more I think about it the more I realize that I don't really know the difference between 'Do you want' and 'Would you want' unless you follow with some condition (either explicitly or implicitly). 'Would you like to eat breakfast, if I made French toast?'