I have been predicting for a while that the price and positioning of the 4 series would be a greater increment from the 3 series a la the 5/6 differential. Expect a more richly trimmed interior and a few other goodies for the extra money. I think the grand coupe will be popular as it brings this concept down to a more manageable sized car for those who drive on narrow streets.
The skepticism on weight reductions seems well founded. Standard carbon fiber brake disks would knock the price out of the ballpark. Remember, the cost of high performance automobiles will increase more rapidly than for the regular cars because of unreasonable government regulations on fuel efficiency. Manufacturers will ration the available vehicles with high prices. It is already here. The V8 upgrade in a Mustang GT is over $8000 because the car really does not come with any other enhancements except for suspension tuning. That is a pretty big percentage of the price of a $35k car.