My take on KITT would be:
1. Yes, stay as an everday sports car, but pushing a bit on the futuristic edge, say 3-4 years ahead of design.
2. Doesn't necessarily have to be an all american car, as long as it has the distinctive custom KITT nose, scanner, resembling car body and an interior that screams Knight Rider - such as the Acura NSX concept, which is coming very very close to a modern version of KITT. Design lineage of KITT IS A MUST!
3. KITT's voice should be the same - I know, William Daniels' voice has aged, since I heard him on CC Roast of DH, but there are surely voice actors, who comes close to his voice.