Nope, it's not as sexy as it sounds, sorry.
I'm going to cheat and give you TWO diabetes fantasy devices, just to make a point.
Fantasy Device #1: A glucometer that is accurate. I've said it before, and I'll say it again. If we can drive a remote control car on freaking mars, why can't we have a blood sugar meter that has better than +/- 20% accuracy? To me it is kind of sad and pathetic that when someone says "what is your diabetes fantasy device?" my answer is so basic. But I really, truly, honestly, fervently, with all my heart and soul believe that an accurate glucose meter would make such a huge difference in my blood glucose control and my quality of life.
Ok, I'll get off my soap box now and give you the fantasy device you really want to hear about.
Fantasy Device #2: A camera/i-Pod/smart phone app that lets you take a picture of your plate and whatever food is on it, and can some how accurately tell you the amount of carbs your meal has in it. Wouldn't that be awesome?! Can't you just imagine it? You sit down at a restaurant, pull out your cell phone, snap a picture of your plate, and ding! "Your meal contains 65 grams of carbohydrates." It would be amazing!