If this is Full Frame and under $2500 I would crap myself in shock and happiness and preorder one without even thinking.
Unfortunately, I think it will be the sensor from the G1X.
I was very happy to see the 1.85x sensor in the G1X, but for a mirrorless system, i'm full frame or bust. Since getting my 5D Classic I'm in love with Full Frame like it's film era photography and I'm not going back.
I really hope that there is 3 models/grades of the Canon Mirrorless system as has been talked about before. G1X sensor size being the entry level, 1.6x/APS-C being the prosumer/upgrade, and FF being the pro version. This would be groundbreaking and awesome. If Canon plans to do this, I hope they announce it soon before I switch to the(hopefully soon to come) D600. This is one time where I think announcing products in development would really help the brand.