I think after all the rumors settle, you have to think economically. I think the BMW would either have a variant on the I6 but most like will be a variant of the now 540I. (4 liter V8) It won't be cost effective for BMW to just use the 540 engine on the 7 and 5 series. The 3 series is just killing the sales of the 5 and the 7. If i belive to be right, the M5 is the same engine as the 540 but tuned? So it could be a detuned version of the M5 engine.