Well... going back to the A8 for a second ? I've made a very quick modification of the current A8... which I think would make it look a lot better.
Small change... just removed the "tooth" from the headlamp.
And here I moved the front axle a bit to the front.
I don't know why they added that "tooth" here. It just doesn't fit here.
Anyway, since you are talking about the platforms I also think something like the PPC platform would be the best option. Just like the new BMW 7 series Audi could also give us an option to choose between classic ICE, PHEV or fully Electrioc versions of the next A4, A5, A6, A7 and A8 generations (and SUVs).