The 4 Series will share the 3 and 4 series drivetrains but be the premier car in that segment similar to how the 6 Series Gran Coupe is situated. An M version is likely in the cards as well as the 6 Series Gran Coupe also gets an M version based on the M6. Naturally, this one would be based on the M3/M4.
So we will have a 3 Series sedan, wagon, GT, and a 4 Series coupe, convertible, and Gran Coupe. We don't think any more variants are possible but will not count out BMW who seems to come up with a new one every other week. If this car is as good looking as it's 6 Series big brother and priced well, it will likely be a hit.