>just take the V-12 from Lambo, and tune it for a luxo sedan.
>

It's not that simple. The Murcielago's V12 wouldn't have fit in the A8. Plus,
they can't produce them in great enough number for A8 application.

>I understand the width & length angle, but what are any benefits, between
>some savings in development time, and small size.

FITMENT. The A8 wouldn't have accpeted a V-12 of that displacement.

> they seem to be a little
>low on power compared to a "traditional" layout,

This is the result of Adui's tuning, not the engine type.

> and they seem to have a
>little more harshness vibration.
>

B.S. I've ridden in a W12 Pheaton and it was incredible.