Funny you say that, Audit really started to take off back in the early 00's when VW was pumping out crazy numbers on their MKIV Golf platform, that was the peak of parts sharing and all that, MB even took an L w/ the Chrysler merger and the shyt cars that they made back then as well.
Audi's always been a brand with its own models though (albeit owned by VW, even back in the early 90's there was Porsche parts on Audi's and VW's

), dating back to the 80's, but if you Audi money back in the 80's, you were really doing something. But they were always driven by technology. Quattro from their racing background really separated them. That's what it'll take for Lexus to come through.
And I will agree, I love my 2.0T in my GTI, but an A5 is far too heavy of a car for that engine. And I would say that the 1st and 2nd Gen IS is one of my favorite cars, along w/ the 1st and 2nd Gen GS. Lexus is known for reliability, quiet and resale, that's their place until they can prove otherwise.