CART or modern indycar pack would indeed be great and I've suggested both myself, but when it comes to experience, I see one very big problem. For modern Indycar, for example, half of the season tracks are ovals. And doing good oval AI is wholly another beast compared to road course racing and no one since Papyrus and NR2003 has achieved a really good oval AI. I have high hopes for rF2 pulling it through, it shows some promise, but so far it lacks far behind their excellent road course AI. It only shows that you need fully new logic for oval racing. Rule system for ovals are also completely different and proper working yellows and caution rules are pretty much a necessity for good racing, unless you want chaos.
for this we would need a lot of new tracks ... would be nice but I think it's unrealistic at the moment ... the same like a full Trans Am Series or a Stock Car Series ... car set = maybe, experience = hardly