Remember people that there's no distinction between Standard and Premium anymore. All cars that were premium in GT5 will be premium in GT6. They just added 125+ more.
As for the missing NSX being apart of the Vision GT lineup. I don't think so. Those cars, for the most part seem to be being kept under wraps until revealed the the exception of a couple like BMW's. While the new NSX is a GT car, the point of creating a Vision GT car would be to create a car without limits. Besides, known about the NSX since Iron Man 3.
EDIT: The Base cars, for those who don't know, are the carbon cars from GT4 and GT5. One WAS shown in the new trailer. But they look like this:
Proof: