Well....if it's possible to scan an old kit, or parts thereof, it's also possible to scan pieces which are created or were modified by a creative modeler, just as the tooling model craftsmen, carved from wood back in the day.
So just for argument's sake, a guy takes an annual Jo-Han '70 GTX, mates it with the underpinnings of an Ertl designed late sixties B-Body and modifies the interior, then scans all the parts, refines it some more in the 3D program, test prints the outcome and if ok, sends the file to China to tool.
The technology is there and in part being used by the aftermarket, only thus far the big hurdle is, tooling dollars, the fear of losing your shirt if the ROI isn't there. This is what separates the men from the boys
Just my 2 cents and as always open for input.
Cheers
Luc