Some more technical info
The i8 has a 1.5liter 3-cylinder engine with 300Nm. Compare that with the new N20 (X1, X3 etc) engine which has 2liter 4-cylinder and 350Nm. So the i8 has 1 cylinder less and 14% higher cylinder torque than the N20.
So the trend seems to be the following:
Step 1: downsize the engine and compensate with turbo boost. This is being done now on several models. Example: from X3 6-cylinder 3liter N52 28i to 4-cylinder 2liter N20 28i. This reduces fuel consumption.
Step2: downsize more and compensate acceleration with electrical generator/motor, which can also be used for brake energy recovery.