The trend to downsize from large capacity engines to smaller capacity forced induction engines has been going on for a good couple of years now to meet stringent emission rules. The current 4 Series has been around 5 years now and the only non 4 cylinder petrol engines in it were the 435i/440i and M cars. The 430i superseded the 428i which was also a 4 cylinder turbo unit. Same with the current 5 Series, the 530e and 530i are both 4 cylinder turbo petrol units.

The next 1 Series will be front wheel drive too.