Size reduction compared to what?The Rebels could be more ergonomic, but they don't have to be bigger necessarily... Just give the grip a different form (a little bit thicker...)
I don't think going to be good if it is smaller than T2. Once you hold D90 or 50D in your hands they feel just about right. Going a bit thinner couldn't hurt but only to cca Rebel dimensions ~6cm
IMO give us a bit <50D body, FF, and HD EVF and call it a day...
Next upgrade: global shutter.
I'm still wondering how Canon wants to seperate from EP-1, GF1 and so on... only with the capability of using EF/EF-S lenses?