If they added an importer to import cars from previous versions of the game, with a comment about them not running at as good of graphics as the game itself. I’m guessing 5 & 6 use the same data format as 7 does.
They could even go back to 4, 3, 2, and probably 1. Also even the Horizon series too…
It could scan the disk [required] and bring in all the cars that do not exist in 7. Then add them to the cars available for purchase…
They would have to rename cars that they no longer have the license for similar to what GTA does.
In other words, a simple port can’t happen due to legality.
In other cases it’s cars that really don’t matter anymore. Like replacing a 2015 Audi with a 2017 of identical model.
Wouldn’t work as licensing in many cases is title specific.
Either way, an excellent suggestion for the features wish list you can find a link to at the top of the page.
They’ve said repeatedly over the years that they won’t add assets of substandard quality. Same deal with 60fps. This is a non-starter issue for Turn 10 philosophy, to say nothing of the licensing issues and need to recalculate PI and parts options.