The engine noises I heard from the BMW i8 were ridiculous - not that they were bad but just because it seems so childish. It's like you're a 5-year-old sat on a chair making BROOM! BROOM! noises.
An example is on this YouTube video [0]. First you can hear the electric acceleration, then the driver then slows down and switches on the engine noise. It even simulates the noise of gear changes...
You already do get a lower level of feedback from the noise of the electic motor. It doesn't make much noise but it does change in pitch as you go faster. Plus you have the speedometer and the colour of the dashboard changes colour I think as you speed up.
An example is on this YouTube video [0]. First you can hear the electric acceleration, then the driver then slows down and switches on the engine noise. It even simulates the noise of gear changes...
[0]: https://youtu.be/yerTSDJtJmM?t=6m29s