Pix / drawings of the the i8 appeared in CAR magazine months ago, I forget which months issue. I do have to admit that the CAR renderings make the concept appear a little less..."chunky"?
The " i " sub-brand is a supposed offshoot (ala Mini), of the main BMW brand. The " i " cars / vehicles will all be engineered to use new technologies and in particular to up the fuel efficiency of BMW. Think of them as the BMW Prius....which is also about to become a (sub)brand, like Scion is to Toyota. I am probably wrong about this, but the 8 has nothing to do with the cylinder count of the engine.
EDIT....
I just did a Yahoo search of the i8 and BMW's own website tells you quite a bit about the i8. It is a plug-in hybrid that uses an electric motor to drive the front wheels and at some point, when needed, a 3 cylinder gas engine will kick in to up available power/recharge the batteries? The 3 cylinder is rated (currently, as this is a prototype) at 220 horsepower.
I guess another way to look at the i8 is that it's the BMW Volt.